FOOTNOTES:

Encysted in chylific stomach and gizzard; free in large intestine.Ref.—Siebold, Naturg. wirbelloser Thiere, pp. 56, 71 (1839); Stein, Müll. Arch., 1848, p. 182, pl. ix., figs. 38, 39; Leidy, Trans. Amer. Phil. Soc., Vol. X., p. 239 (1852); Bütschli, Zeits. f. wiss. Zool., Bd. XXI., p. 254 (1871), and Bd. XXXV., p. 384 (1881); Schneider, Grégarines des Invertébrés, p. 92, pl. xvii., figs. 11, 12 (1876).

Encysted in chylific stomach and gizzard; free in large intestine.

Ref.—Siebold, Naturg. wirbelloser Thiere, pp. 56, 71 (1839); Stein, Müll. Arch., 1848, p. 182, pl. ix., figs. 38, 39; Leidy, Trans. Amer. Phil. Soc., Vol. X., p. 239 (1852); Bütschli, Zeits. f. wiss. Zool., Bd. XXI., p. 254 (1871), and Bd. XXXV., p. 384 (1881); Schneider, Grégarines des Invertébrés, p. 92, pl. xvii., figs. 11, 12 (1876).

Nyctotherus ovalis, Leidy.Infusoria.

Small and large intestines.Ref.—Leidy, Trans. Amer. Phil. Soc., Vol. X., p. 244, pl. xi. (1852).

Small and large intestines.

Ref.—Leidy, Trans. Amer. Phil. Soc., Vol. X., p. 244, pl. xi. (1852).

Plagiotoma (Bursaria) blattarum, Stein.Infusoria.

Rectum.Ref.—Stein, Sitzb. d. königl. Böhm. Ges., 1860, pp. 49, 50.

Rectum.

Ref.—Stein, Sitzb. d. königl. Böhm. Ges., 1860, pp. 49, 50.

Lophomonas Blattarum, Stein.Infusoria.

Rectum.Ref.—Stein (loc. cit.); Bütschli, Zeits. f. wiss. Zool., Bd. XXX., p. 258, plates xiii., xv. (1878).

Rectum.

Ref.—Stein (loc. cit.); Bütschli, Zeits. f. wiss. Zool., Bd. XXX., p. 258, plates xiii., xv. (1878).

L. striata, Bütschli.Infusoria.

Rectum.Ref.—Bütschli, Zeits. f. wiss. Zool., Bd. XXX., p. 261, plates xiii., xv. (1878).

Rectum.

Ref.—Bütschli, Zeits. f. wiss. Zool., Bd. XXX., p. 261, plates xiii., xv. (1878).

Gordius, sp.Nematelmintha.

Specimens in the Museum at Hamburg, from Venezuela. Obtained from some species of Cockroach.

Oxyuris Diesingi, Ham.Nematelmintha.

Rectum, frequent.Ref.—Hammerschmidt, Isis, 1838; Bütschli, Zeits. f. wiss. Zool., Bd. XXI., p. 252, pl. xxi. (1871).

Rectum, frequent.

Ref.—Hammerschmidt, Isis, 1838; Bütschli, Zeits. f. wiss. Zool., Bd. XXI., p. 252, pl. xxi. (1871).

O. Blattæ orientalis, Ham.Nematelmintha.

Rectum (much rarer thanO. Diesingi).Ref.—Hammerschmidt (loc. cit.); Bütschli, Zeits. f. wiss. Zool., Bd. XXI., p. 252, pl. xxii. (1871).

Rectum (much rarer thanO. Diesingi).

Ref.—Hammerschmidt (loc. cit.); Bütschli, Zeits. f. wiss. Zool., Bd. XXI., p. 252, pl. xxii. (1871).

Other species ofOxyurisare said to occur in the same situation,

e.g.,O. gracilisandO. appendiculata(Leidy, Proc. Acad. N. S. Phil., Oct. 7th, 1879), andO. macroura(Radkewisch, quoted by Van Beneden in Animal Parasites, Engl. trans., p. 248).

Filaria rhytipleurites.Nematelmintha.

Encysted in the fat-body of the Cockroach; sexual state in the alimentary canal of the Rat.Spiroptera obtusais similarly shared by the Meal-worm (larva ofTenebrio molitor) and the Mouse.Ref.—Galeb, Compt. Rend., July 8th, 1878.

Encysted in the fat-body of the Cockroach; sexual state in the alimentary canal of the Rat.Spiroptera obtusais similarly shared by the Meal-worm (larva ofTenebrio molitor) and the Mouse.

Ref.—Galeb, Compt. Rend., July 8th, 1878.

Acarus, sp.Arachnida.

Found by Cornelius upon the sexual organs of a male Cockroach.Ref.—Cornelius, Beitr. zur nähern Kenntniss vonPeriplaneta orientalis, p. 35, fig. 23 (1853).

Found by Cornelius upon the sexual organs of a male Cockroach.

Ref.—Cornelius, Beitr. zur nähern Kenntniss vonPeriplaneta orientalis, p. 35, fig. 23 (1853).

Evania appendigaster, L.Insecta(Hymenoptera).

A genus of Ichneumons, parasitic uponPeriplanetaandBlatta.Ref.—Westwood, Trans. Ent. Soc., Vol. III., p. 237; Ib., Ser. II., Vol. I., p. 213.

A genus of Ichneumons, parasitic uponPeriplanetaandBlatta.

Ref.—Westwood, Trans. Ent. Soc., Vol. III., p. 237; Ib., Ser. II., Vol. I., p. 213.

Symbius Blattarum, Sund.Insecta(Coleoptera).

The apterous female is parasitic uponP. americanaandB. germanica.Ref.—Sundevall, Isis, 1831.

The apterous female is parasitic uponP. americanaandB. germanica.

Ref.—Sundevall, Isis, 1831.

SENSE OF SMELL IN INSECTS.

Since the printing of the sheets which describe the organs of special sense, we have become acquainted with two experimental researches of recent date, instituted for the purpose of determining whether other organs, besides the antennæ, may be specially concerned with the perception of odours by Insects.

Prof. Graber (Biol. Centralblatt, Bd. V., 1885) has described extensive and elaborate experiments upon various Insects, tending to the conclusion that the palps and the cerci may be sensitive to odours, and that in special cases the palps may be even more sensitive in this respect than the antennæ. Cockroaches, decapitated, but kept alive for some days, were found to perceive odours by means of their cerci. His general conclusion is that Insects have no special sense of smell, but that various parts of the surface of the body are furnished with nerve-endings capable of perceiving strong odours. Prof. Graber’s results are known to us only through the abstract given by Prof. Plateau in the paper next to be mentioned.

Prof. Plateau (Compt. rend. de la Soc. Entom. de Belgique, 1886) relates experiments upon the powers of scent resident in different organs of the Cockroach. Two Cockroaches had their palps (maxillary and labial) removed; two others had the antennæ removed. An evaporating dish, 8 inches in diameter, was then partly filled withfine sand. In the centre of the dish was set a circular box of card, without bottom, 2 inches in diameter, and14/5inches high. In this box bread moistened with beer, a bait very attractive to Cockroaches, was placed, and renewed daily. The four Cockroaches were allowed to run about in the dish outside the box, and to feed upon the bread at pleasure by climbing over the enclosure. Observations were made late at night for a month, when it was found that, except on the first night, when the Insects ran all over the dish, none of the Cockroaches without antennæ made their way to the food; while twenty-three times one of the Cockroaches without palps, but with antennæ intact, was found to be feeding; in one instance, both were so found.

Plateau observes that a special sense of smell can only be claimed for organs which are able to detect faint and distant odours, and that experiments made with powerful odours close to the body of the Insect may lead to fallacious results. The perception of faint odours cannot be effected by the palps or cerci of the Cockroach, but only by the antennæ.

THE END.

Printed by McCORQUODALE & CO, Limited, Leeds.

FOOTNOTES:1Baer’s account of Döllinger is to be found in the Leben und Schriften von K. E. von Baer, § 8.2Prof. Plateau’s chief communications will be found on pp.131and159; Mr. Nusbaum has furnished the account of the Development of the Cockroach, pp.180to 195; and Mr. Scudder the Geological History of the Cockroach, chap. xi.3Correspondence of John Ray, p.142.4Copies dated 1762 have a plate representing the microscope and dissecting instruments used by the author.5Dufour. Rech. anat. et phys. sur les Hémiptères (1833) les Orthoptères, les Hymenoptères et les Neuroptères (1841), et les Diptères (1851). Mém. de l’Institut, Tom. IV., VII., XI. Also many memoirs in Ann. des Sci. Nat.6Newport. Art. “Insecta,” in Cycl. of Anat. and Phys. (1839), besides many special memoirs in the Phil. and Linn. Trans.7Leydig. Vom Bau des Thierischen Körpers (1864), Tafeln zur vergl. Anatomie (1864), Untersuchungen zur Anat. und Histologie der Thiere (1883), &c., besides many special memoirs in Müller’s Archiv., Zeits. f. wiss. Zool., Nova Acta, &c.8In some Insects there are traces of a fourth thoracic segment.9So also in some larvæ (Calandra,Œstrus, &c.).10In some aquatic Insects the exchange of gases is effected by “pseudobranchiæ,” and the tracheal system is closed.11Dragon-flies have the male copulatory apparatus, but not the genital aperture, in the fore part of the abdomen.12Aphis and Cecidomyia are at times viviparous, and a viviparous Moth has been observed by Fritz Müller (Trans. Entom. Soc. Lond., 1883).13For descriptions of the species Fischer’s Orthoptera Europæa (1853) or Brunner von Wattenwyl’s Nouveau Système des Blattaires (1865) may be consulted. The classification adopted by the last-named author is here summarised.Blattariæ.A.—Femora spinous (Spinosæ).Fam. 1.—Ectobidæ.Seventh abdominal sternum undivided in female. Sub-anal styles absent in male. Wings with triangular apical area.Ectobia, includingE. lapponica(Blatta) and other genera.Fam. 2.—Phyllodromidæ.Seventh abdominal sternum undivided in female. Sub-anal styles usual in male (0 or rudimentary inPhyllodromia). Wings without triangular apical area.Phyllodromia, includingP. germanica(Blatta) and other genera.Fam. 3.—Epilampridæ.Fam. 4.—Periplanetidæ.Seventh abdominal sternum divided in female. Sub-anal styles conspicuous in male.Polyzosteria,Periplaneta, &c.B.—Femora not spinous (Muticæ).Families.—Chorisoneuridæ,Panchloridæ,Perisphæridæ,Corydidæ,Heterogamidæ,Blaberidæ,Panesthidæ.Many useful references will be found in Scudder’s Catalogue of N. American Orthoptera, Smiths. Misc. Coll., viii. (1868).14Linnæus was certainly mistaken in his remark (Syst. Nat., 12th ed.) that this species is native to America, and introduced to the East—“Habitat in America: hospitatur in Oriente.” He adds, “Hodie in Russiæ adjacentibus regionibus frequens; incepit nuperis temporibus Holmiæ, 1739, uti dudum in Finlandia.”15This must have been the “San Felipe,” a Spanish East Indiaman, taken in 1587. See Motley, United Netherlands, Vol. II., p. 283.16Biblia Naturæ, Vol. I., p. 216.17De Borck. Skandinaviens rätvingade Insekters Nat. Hist., I., i., 35.18Brunner. N. Syst. d. Blattaires, p. 234.19Scudder. Proc. Boston Soc. N.H., Vol. XIX., p. 94.20For example, the Russians often call itProussaki, the Prussian Cockroach, and believe that their troops brought it home with them after the Seven Years’ War. The native Russian name isTarakan. In Finland and Sweden the same species is calledTorraka, which appears to be a corruption of the Russian word, and confirms the account of Linnæus quoted above.B. germanicais found in the United States from the Atlantic to the Pacific. It is generally known as the Croton Bug, because in New York it is often met with about the water pipes, which are supplied from the Croton River (Dr. Scudder).21Bell’s Edition, Vol. I., p. 454.22British Museum Catalogue of Blattariæ (1868) and Supplement (1869). It is probable that the number is over-estimated in this catalogue, the same species being occasionally renamed.23Brongniart has just described a Carboniferous Insect which he considers a Thysanuran (Dasyleptus Lucasi), though it has but one anal appendage. See C. R. Soc. Ent., France, 1885.24Hummel, loc. cit.25The use of the termpupato denote the last stage before the complete assumption of wings in the Cockroach, is liable to mislead. There is no resting-stage at all; wings are developed gradually, and are nearly as conspicuous in the last larval state as in the so-called pupa. There seems no reason for speaking of pupæ in this case.It is preferable to designate as “nymphs” young and active Insects, immature sexually, but with mouth-parts like those of the adult. See Lubbock, Linn. Trans., 1863, and Eaton, Linn. Trans., 1883.26SeeAppendix.27Insectorum Theatrum, p. 138. The nameSchwabeis frequent in Franconia, where it is believed to have taken origin. Suabia adjoins Franconia, to the south.28Compare the Swedish name (supra, p.18).29A fuller list of vernacular names is given by Rolland, Faune Populaire de la France, Vol. III., p. 285. See also Nennich, Polyglotten Lexicon, Vol. I., p. 620.30Anatomy of the Blow-fly, p.11.31Q. J. Micr. Sci., 1871, p. 394.32Krukenberg. Vergl. Physiologische Vorträge, p. 200. Halliburton, Q. J. Micr. Sci., 1885, p. 173.33Ann. d. Chem. u. Pharm., Bd. 98.34Previously observed by Leydig inCorethra.35A condensed and popular account of these researches will be found in Semper’s Animal Life, p. 20.36Prof. Huxley (Anat. Invert. Animals, p. 419) states that the integument splits along the abdomen also, but this is a mistake.37Audouin. Rech. anat. sur le thorax des Insectes, &c. (Ann. Sci. Nat., Tom I., p. 97. 1824.)38This application of the word to denote parts intermediate between terga and sterna has become general since its adoption by Audouin. It appears also in the older and deservedly obsolete nomenclature of Kirby and Spence. Professor Huxley has unfortunately disturbed the consistent use of this term by giving the namepleurato the free edges of the terga in Crustacea.39Where the thorax apparently consists of four somites, as in some Hymenoptera, Hemiptera, Coleoptera, and Lepidoptera, the first abdominal segment has become blended with it.40Balfour. Embryology, Vol. I., p. 337.41E.g., by Graber. Insekten, Vol. II., p. 423.42See, for example, Huxley on the Crayfish.43One of the few points in which we have to differ from the admirable description of the Cockroach given in Huxley’s Comparative Anatomy of Invertebrated Animals, relates to the articulation of the mandible, which is there said to be carried by the gena.44Morphologie des Tracheen-systems, p. 103.45Zaddach, Entw. des Phryganiden Eies, p. 86; Rolleston, Forms of Animal Life, p. 75, &c.46Zeits. f. wiss. Zool., Bd. XVI., pl. vii., fig. 33.47Insekten, Vol. II., p. 508.48Anat. Invert. Animals, p. 398.49Professor Huxley has proposed to call the attached basehypopharynx, and the free tiplingua.50Professor J. Wood-Mason points out that inMachilis(one of the Thysanura) the mandible shows signs of segmentation, while the apical portion is deeply divided into an inner and an outer half. Ripe embryos ofPanesthia (Blatta) javanicaare said to exhibit folds which indicate the consolidation of the mandible out of separate joints, while the cutting and crushing portions of the edge are divided by a “sutural mark,” which may correspond to the line of junction of the divisions of a biramous appendage (Trans. Ent. Soc., 1879, pt. 2, p. 145).51The homology of the labium with the first pair of maxillæ is in no other Insects so distinct as in the Orthoptera.52Rosenthal, Ueb. d. Geruchsinn der Insekten. Arch. f. Phys. Reil u. Autenrieth, Bd. X. (1811). Hauser, Zeits. f. wiss. Zool., Bd. XXXIV. (1880).53Mém. Acad. Roy. de Belgique, Tom. XLI. (1874). Prof. Plateau’s writings will often be referred to in these pages. We owe to him the most important researches into the physiology of Invertebrates which have appeared for many years.54Exp. sur le Rôle des Palpes chez les Arthropodes Maxillés. Pt. I. Bull. Soc. Zool. de France, Tom. X. (1885).55Leydig, Taf. z. vergl. Anat., pl. x., fig. 3. Hauser, Zeits. f. wiss. Zool., Bd. XXXIV., p. 386. Jobert has figured the sensory organs of the maxillary palps of the Mole-cricket (Ann. Sci. Nat., 1872), and Forel similar organs in Ants (Bull. Soc. Vaudoise, 1885).56The reader who desires to follow this subject further is recommended to study chap. vi. of Graber’s Insekten, which we have found very useful.57Freshwater Crustacea, however, are sometimes similar to their parents at the time of hatching.58InDytiscusthe mandibles are perforate at the base, and not at the tip. See Burgess in Proc. Bost. Soc. Nat. Hist., Vol. XXI., p. 223.59Ein Käfer mit Schmetterlingsrüssel, Kosmos, Bd. VI. We take this reference from Hermann Müller’s Fertilisation of Flowers.60An interesting account of the structure and mode of action of the Bee’s tongue is to be found in Hermann Müller’s Fertilisation of Flowers, where also the evolution of the parts is traced through a series of graduated types.61See Newport’s figure of Vanessa atalanta (Todd’s Cyc., Art. Insecta), or Burgess on the Anatomy of the Milk-weed Butterfly, in Anniversary Mem. of Boston Soc. Nat. Hist., pl. ii., figs. 8–10 (1880).62Balfour, Embryology, Vol. I., p. 337.63Huxley, Med. Times and Gazette, 1856–7; Linn. Trans., Vol. XXII., p. 221, and pl. 38 (1858).64“I think it is probable that these cervical sclerites represent the hindermost of the cephalic somites, while the band with which the maxillæ are united, and the genæ, are all that is left of the sides and roof of the first maxillary and the mandibular somites.”—Huxley, Anat. Invert. Animals, p. 403.65Balfour, Embryology, Vol. I., note to p. 337.66J. S. Kingsley in Q. J. Micr. Sci. (1885), has reviewed the homology of Insect, Arachnid, and Crustacean appendages, and comes to conclusions very different from those hitherto accepted. He classifies the appendages as pre-oral (Insect-antennæ) and post-oral, and makes the following comparisons:—Hexapoda.Acerata.Crustacea.(=Insecta + Myriopoda?)(=Arachnida + Limulus.)(1) Antennæ.Absent.Absent.(2) Mandibles.Cheliceræ.Antennules.(3) Maxillæ.Pedipalpi.Antennæ.(4) Labium.1st pair legs.Mandibles.(5) 1st pair legs.2nd pair legs.1st Maxillæ.(6) 2nd pair legs.3rd pair legs.2nd Maxillæ.(7) 3rd pair legs.4th pair legs.1st Maxillipeds.Pelseneer (Q. J. Micr. Sci., 1885), concludes that both pairs of antennæ are post-oral inApus, and probably in all other Crustacea.67Many Orthoptera, which seize their prey with the fore legs, have a very long pronotum.68Also inPhasmidæ(see Scudder, Psyche, Vol. I., p. 137).69Professor Huxley (Anat. Invert. Animals, p. 404) points out that the so-calledpulvillusought to be counted as a sixth joint. The same is true of the foot of Diptera and Hymenoptera, where there are six tarsal joints, the last carrying the claws. (Tuffen West on the Foot of the Fly. Linn. Trans., Vol. XXIII.)70The nomenclature adopted by Packard (Third Report of U.S. Entomological Commission) seems to us open to theoretical objections.71On wing-plaiting and wing-folding in Blattariæ see Saussure, Etudes sur l’aile des Orthoptères. Ann. Sci. Nat., Sér. 5e(Zool.), Tom. X.72Grundzüge der Vergl. Anat. (Arthropoden, Athmungsorgane.)73Origin and Metamorphoses of Insects, p. 73.74Palmén cites one striking proof of the low position of Ephemeridæ among Insects. Their reproductive outlets are paired and separate, as in Worms and Crustacea.75These examples are cited by Palmén.76Eaton, Trans. Ent. Soc., 1868, p. 281; Vayssière, Ann. Sci. Nat., Zool., 1882, p. 91.77Zur Morphologie des Tracheensystems (1877).78We take these instances from Eaton, Monograph of Ephemeridæ, Linn. Trans., 1883, p. 15.79Charles Brongniart has lately described a fossil Insect from the Coal Measures of Commentry, which he namesCorydaloides Scudderi, and refers to the Pseudo-Neuroptera. In this Insect every ring of the abdomen carries laminæ, upon which the ramified tracheæ can still be made out by the naked eye. Stigmata co-existed with these tracheal gills. (Bull. Soc. Sci. Nat. de Rouen, 1885.)Some Crustacea are furnished with respiratory leaflets, curiously like those of Tracheates, with which, however, they have no genetic connection. In Isopod Crustacea the exopodites of the anterior abdominal segments often form opercula, which protect the succeeding limbs. In the terrestrial Isopods,PorcellioandArmadillo, these opercula contain ramified air-tubes, which open externally, and much resemble tracheæ. The anterior abdominal appendages ofTylusare provided with air-chambers, each lodging brush-like bundles of air-tubes, which open to the outer air. Lamellæ, projecting inwards from the sides of the abdominal segments, incompletely cover in the hinder part of the ventral surface of the abdomen, and protect the modified appendages. (Milne Edwards, Hist. Nat. des Crustacés, Vol. III.)80Gerstaecker has found in the two first abdominal segments ofCorydia carunculigera(Blattariæ) pleural appendages, which are hollow and capable of protrusion. They have no relation to the stigmata, which are present in the same segments, and their function is quite unknown. See Arch. f. Naturg., 1861, p. 107.81Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera); in the Earwig they become modified and form the forceps. The “caudal filaments” ofApusare curiously like cerci.The cerci are concealed in the AmericanCryptocercus, Scudd. (Fam.Panesthidæ).82Entw. der Biene. Zeits. f. wiss. Zool. Bd. XX. Or, see Balfour’s Embryology, Vol. I., p. 338.83From more recent observations it is probable that abdominal appendages are usually present in the embryos of Orthoptera, Coleoptera, Lepidoptera, and possibly Hymenoptera. The subject is rapidly advancing, and more will be known very shortly.84See, for example, Klein’s Elements of Histology, chap. ix.85The exceptions relate chiefly to the alary muscles of the pericardial septum. Lowne (Blow-fly, p. 5, and pl. v.) states that some of the thoracic muscles of that Insect are not striated.86For example, Prof. Huxley, in his Anatomy of Invertebrated Animals (p. 254), says that “as the hard skeleton [of Arthropods] is hollow, and the muscles are inside it, it follows that the body, or a limb, is bent towards that side of its axis, which is opposite to that on which a contracting muscle is situated.” The flexor muscles of the tail of the Crayfish, which, according to the above rule, should be extensors, the muscles of the mandibles of an Insect, and the flexors and extensors of Crustacean pincers are among the many conspicuous exceptions to this rule.87Haller. This and other examples are taken from Rennie’s Insect Transformations.88Bull. Acad. Roy. de Belgique, 2e.Sér., Tom. xx. (1865), and Tom. xxii. (1866).89Loc. cit. 3e.Sér., Tom. vii. (1884). Authorities for the various estimates are cited in the original memoir.90Klassen und Ordnungen des Thierreichs, Bd. V., pp. 61–2.91This change in the relation of weight to strength, according to the size of the structure, has long been familiar to engineers. (See, for example, “Comparisons of Similar Structures as to Elasticity, Strength, and Stability,” by Prof. James Thomson, Trans. Inst. Engineers, &c., Scotland, 1876.) The application to animal structures has been made by Herbert Spencer (Principles of Biology, Pt. II., ch. i.). The principle can be readily explained by models. Place a cubical block upon a square column. Double all the dimensions in a second model, which may be done by fitting together eight cubes like the first, and four columns, also the same as before except in length. Each column, though no stronger than before, has now to bear twice the weight.92Contractile force varies as sectional area of muscle. LetWbe weight of Horse;w, weight of Bee;R, a linear dimension of Horse;r, a linear dimension of Bee. Then,Contr. force of Hors eContr. force of Bee=sect. area of muscles (Horse )sect. area of muscles (Bee)=R2r2.But sinceWw=R3r3,R2r2=Ww×rR.ThereforeContr. force of HorseContr. force of Bee=WrwRBut, by definition,Rel. m.f. of HorseRel. m.f. of Bee=Contr. f. of HorseWContr. f. of Beew=Contr. f. of HorseContr. f. of Bee×wW=WrwR×wW=rR=r3R313=wW13.The weight of a horse is about 270,000 grammes, that of a bee ·09 gramme; so thatwW13=·09270,00013=·000,000,3̅13= ·0015 (nearly) =Calculated Ratio of Relative Muscular Force of Horse to that of Bee. The Observed Ratio (Plateau) is·523·5= ·02128; so that the relative muscular force of the Horse is more than fourteen times as great in comparison with that of the Bee as it would be if the muscles of both animals were similar in kind, and the proportions of the two animals similar in all respects.93Rech. sur la Force Absolue des Muscles des Invertébrés. IePartie. Mollusques Lamellibranches. Bull. Acad. Roy. de Belgique, 3eSér., Tom. VI. (1883).Do., IIePartie. Crustacés Décapodes. Ibid., Tom. VII. (1884).94Statical muscular forceandSpecific muscular forceare synonymous terms in common use.Contractile force per unit of sectional areagives perhaps the clearest idea of what is meant.95Vol. II., p. 203. The calculation here quoted is based upon an observation of Swammerdam, who relates that a Cheese-hopper,1/4in. long, leaped out of a box 6 in. deep.96Haughton’s Animal Mechanics, 2nd ed., p. 43.97In any comparison it is necessary to cite not the height cleared by the man, but the displacement during the leap of his centre of gravity.98The granules are not shown in the figure, having been removed in the preparation of the tissue for microscopic examination.99Balfour, Embryology, Vol. II., p. 603.100Yung (“Syst. nerveux des Crustacées Décapodes, Arch. de Zool. exp. et gén.,” Tom. VII., 1878) proposes to nameconnectivesthe longitudinal bundles of nerve-fibres which unite the ganglia, and to reserve the termcommissuresfor the transverse communicating branches.101This commissure, which has been erroneously regarded as characteristic of Crustacea, was found by Lyonnet in the larva of Cossus, by Straus-Dürckheim in Locusta and Buprestis, by Blanchard in Dytiscus and Otiorhynchus, by Leydig in Glomeris and Telephorus, by Dietl in Gryllotalpa, and by Liénard in a large number of other Insects and Myriapods, including Periplaneta. See Liénard, “Const. de l’anneau œsophagien,” Bull. Acad. Boy. de Belgique, 2eSér., Tom. XLIX., 1880.102We have not been able to distinguish in the adult Cockroach thedoublelayer of neurilemmar cells noticed by Leydig and Michels in various Coleoptera.103Traité Anat., p. 201, pl. ix., fig. 1.104Phil. Trans., 1834, p. 401, pl. xvi.105Vom Bau des Thierischen Körpers, pp. 203, 262; Taf. z. vergl. Anat., pl. vi., fig. 3.106The stomato-gastric nerves of the Cockroach have been carefully described by Koestler (Zeits. f. wiss. Zool., Bd. XXXIX., p. 592).107“Mem. Acad. Petersb.,” 1835.108“Q. J. Micr. Sci.,” 1879, pp. 340–350, pl. xv., xvi.109“Journ. Quekett Micr. Club,” 1879.110It is to be remarked that unusually large nerves supply the cerci of the Cockroach.111The number in Insects varies from eight to four, but seven is usual; four is the usual number in Crustacea.112“Q. J. Micr. Sci.,” 1885.113Exner has since determined by measurement and calculation the optical properties of the eye of Hydrophilus. He finds that the focus of a corneal lens is about 3mm. away, and altogether behind the eye.114Zur vergl. Phys. des Gesichtsinnes.115A critical history of the whole discussion is to be found in Grenacher’s “Sehorgan der Arthropoden” (1879), from which we take many historical and structural details.116Flies, whose eyes are in several respects exceptional, have almost completely separated rods, notwithstanding their quick sight.117Bull. de l’Acad. Roy. de Belgique, 1885.118References to the literature of the question are given by Hauser in Zeits. f. wiss. Zool., Bd. XXXIV., and by Plateau in Bull. Soc. Zool. de France, Tom. X.119Zeits. f. wiss. Zool., 1885.120Will confirms, by his own experiments (p. 685), Plateau’s conclusion (Supra, p.46), that the maxillary and labial palps have nothing to do with the choice of food.121For a popular account of auditory organs in Insects, see Graber’s Insekten, Vol. I., page 287; also J. Müller, Vergl. Phys. d. Gesichssinn, p. 439; Siebold, Arch. f. Naturg., 1844; Leydig, Müller’s Arch. 1855 and 1860; Hensen, Zeits. f. wiss. Zool., 1866; Graber, Denkschr. der Akad. der wiss. Wien, 1875; and Schmidt, Arch. f. mikr. Anat., 1875.122Here, as generally in the digestive tube of the adult Cockroach, the peritoneal layer is inconspicuous or wanting. It occasionally becomes visible—e.g., in the outer wall of the Malpighian tubules, and in the tubular prolongation of the gizzard.123Plateau has expressed a strong opinion that neither in the stomach of Crustacea nor in the gizzard of Insects have the so-called teeth any masticatory character. He compares them to the psalterium of a Ruminant, and considers them strainers and not dividers of the food. His views, as stated by himself, will be found on p.131.124See Watney, Phil. Trans., 1877, Pt. II. The “epithelial buds” described and figured in this memoir are also closely paralleled in the chylific stomach of the Cockroach.125These epithelial buds have been described as glands, and we only saw their significance after comparing them with Dr. Watney’s account.126Development shows that these tubules belong to the proctodæum, and not to the mesenteron.127The epithelial bands of the rectum of Insects were first discovered by Swammerdam in the Bee (Bibl. Nat., p. 455, pl. xviii., fig. 1). Dufour called them muscular bands (Rech. sur les Orthoptères, &c., p. 369, fig. 44).128“Lehrbuch der Histologie,” p. 337.129Except in Dragon-flies and Ephemeræ.130Zeitsch. f. wiss. Zool., Bd. XXX.131The contents of the Malpighian tubules may be examined by crushing the part in a drop of dilute acetic acid, or in dilute sulphuric acid (10 per cent.). In the first case a cover-slip is placed on the fluid, and the crystals, which consist of oblique rhombohedrons, or derived forms, are usually at once apparent. If sulphuric acid is used, the fluid must be allowed to evaporate. In this case they are much more elongated, and usually clustered. The murexide reaction does not give satisfactory indications with the tubules of the Cockroach.132Bull. Acad. Roy. de Belgique, 1876.133Ib., 1877.134We are indebted to Prof. Plateau for the statement of his views given in the text.135Dissert. de Bombyce, pp. 15, 16 (1669).136Biblia Naturæ, p. 410.137Schrift. d. Marburg. Naturf. Gesellschaft, 1823.138See, for a full account of this discussion, MacLeod sur la Structure des Trachées, et la Circulation Péritrachéenne (1880). The peritracheal circulation was refuted by Joly (Ann. Sci. Nat., 1849).139It may be observed that Graber, who has paid close attention to the heart of Insects, describes the inlets (e. g., inDytiscus) as situated, not at the hinder end, but in the middle of each segment. We have not been able to discover such an arrangement in the heart of the Cockroach.140Lyonnet.141Brandt, Ueb. d. Herz der Insekten u. Muscheln. Mél. Biol. Bull. Acad. St. Petersb. Tom. VI. (1866).142Arch. f. mikr. Anat., Bd. IX. (1872); Insekten, ch. x.143Newport, in Todd’s Cyclopædia of Anatomy and Physiology, Art. Insecta, pp. 981–2.144Beitr. zur näheren Kenntniss von Periplaneta orientalis, p. 19.145The termination of the aorta has been described by Newport, inSphinx(Phil. Trans., 1832, Pt. I., p. 385)Vanessa, Meloe, Blaps and Timarcha. (Todd’s Cycl., Art. “Insecta,” p. 978.)146Moseley, Q. J. Micr. Sci. (1871).147The oldest Tracheate actually known to bear spiracles is the Silurian Scorpion of Gothland and Scotland (Scudder, in Zittel’s Palæontologie, p. 738). We need not say that this is very far removed from the primitive Tracheate which morphological theory requires. The existingPeripatusmakes a nearer approach to the ideal ancestor of all Tracheates, if we suppose that all Tracheates had a common ancestor of any kind, which is not as yet beyond doubt.148The longitudinal air-tubes are characteristic of the more specialised Tracheata. In Araneidæ, many Julidæ, and Peripatus each spiracle has a separate tracheal system of its own.149Investigators are not yet agreed as to the minute structure of the tracheal thread. Chun (Abh. d. Senkenberg. Naturf. Gesells., Bd. X., 1876) considers it an independent chitinous formation, not a mere thickening of the intima. He describes the thread as solid. The intima itself is, he believes, divisible in the larger tubes into an inner and an outer layer, into both of which the thread is sunk. Macloskie (Amer. Nat., June, 1884) describes the spiral as a fine tubule, opening by a fissure along its length. He regards it as a hollow crenulation of the intima, and continuous therewith. Packard (Amer. Nat. Mag., May, 1886) endeavours to show that the thread is not spiral, but consists of parallel thickenings of the intima. He is unable to find proof of the tubular structure, or of the external fissure. We have specially examined the trachea of the Cockroach, and find that the thread can readily be unwound for several turns. It is truly spiral.150It has been supposed that these irregular cells of the tracheal endings pass into those of the fat-body, but the latter can always be distinguished by their larger and more spherical nuclei.151In the first abdominal spiracle the setæ are developed only on that lip which carries the bow.152This subject is treated at greater length in Prof. Plateau’s contribution on Respiratory Movements of Insects. (Infra, p.159.)153Phil. Mag., 1833. Reprinted in “Researches,” p. 44. Graham expressly applies the law of diffusion of gases to explain the respiration of Insects. Sir John Lubbock quotes and comments upon the passage in his paper on the Distribution of the Tracheæ in Insects. (Linn. Trans. Vol. XXIII.)154For an explanation of the physical principles involved in this discussion, and for the calculation (based upon our own assumptions), we are indebted to Mr. A. W. Rücker, F.R.S.155J. Hutchinson, Art. Thorax, Todd’s Cycl. of Anat. and Phys.156De l’absence de mouvements respiratoires perceptibles chez les Arachnides (Archives de Biologie de Van Beneden et Van Bambeke, 1885.)157Ueb. d. Respiration der Tracheaten. Chemnitz (1872).158See table in Burmeister’s “Manual,” Eng. trans. p. 398.159Art. “Insecta,” Cyc. Anat. and Phys., p. 989.160Pogg. Ann. 1872, Hft. 3.161Works, Vol. IX., p. 287. This passage has been cited by Rathke.162Arbeiten a. d. Zool. Zoot. Inst. Würzburg. Bd. II., 1874.163Phil. Trans., 1874, p. 757.164The crystals have been supposed to consist of oxalate of lime (Duchamp, Rev. des sci. nat. Montpellier, Tom. VIII.). Hallez observes that they are prismatic, with rhombic base, the angles truncated. They are insoluble in water and weak nitric acid, but dissolve rapidly in strong sulphuric acid without liberation of gas, and still more rapidly in caustic potash. (Compt. Rend., Aug., 1885.)165It is usually stated that the spermatheca of the Cockroach opens into the uterus, as it does in most other Insects, but this is not true. Locusts and Grasshoppers have the outlet of the spermatheca placed as in the Cockroach; in other European Orthoptera, it lies upon the dorsal wall of the uterus. (Berlese, loc. cit., p. 273.)166It is a striking proof of the sagacity of Malpighi, that he should have observed in the Silkworm the spermatophore of the male (“in spiram circumvolutum persimile semen”) and the spermatheca of the female. His reasoning as to the function of the spermatheca wanted nothing but microscopic evidence of the actual transference of spermatozoa to establish it in all points. Audouin and Siebold supplied what was wanting nearly two centuries later, but they mistook the spirally wound spermatophore for a broken-off penis, and Stein (Weibl. Geschlechtsorgane der Käfer, p. 85) first arrived at the complete proof of Malpighi’s explanation.167The descriptions and figures of the reproductive appendages of female Orthoptera by Lacaze-Duthiers (Ann. Sci. Nat., 1852) are so often consulted, that it may be useful to explain how we understand and name the same parts. In pl. xi., fig. 2, 8′ and 9′ are the 8th and 9th terga; the anterior gonapophyses are seen to be attached to them below;a(figs. 2 and 4) is the base of the same appendage, but the twisted ends are incorrect; the 8th sternum is seen at the back (figs. 2 and 4);a′ represents the outer,fthe inner pair of posterior gonapophyses.168We propose to notice here the chief differences which we have found between the figures of Brehm (loc. cit.), which are the fullest and best we have seen, and our own dissections.Figs. 10, 11 (pp. 169–70). The ejaculatory duct and duct of the conglobate gland are made to end in the penis (infra, p. 178).Figs. 14, 15 (p. 173). These figures seem to us erroneous in many respects, such as the median position of the penis and titillator.Fig. 16 (p. 174). The pair of hooks markedEare too small, and there are additional plates at the base, which are not figured (see our fig.102).F(of our fig.) is omitted.169InBlatta germanicathe testes are functional throughout life. They consist of four lobes each. The vasa deferentia are much shorter than inP. orientalis.170The spermatocysts are peculiar to Insects and Amphibia. They arise by division of the spermatospores, or modified epithelial cells, and form hollow cysts, within which sperm cells (or spermatoblasts) are developed by further division. The sperm cells are usually placed radiately around the wall of the spermatocyst. They escape by dehiscence, and are transformed into spermatozoa.171Huxley, Anat. Invert. Animals, p. 416.172The term “accessory gland,” used by Huxley and others, is already appropriated to glands which we believe to be represented by the utricles of the Cockroach, and which have only a general correspondence with the gland in question.173Similar organs, forming a male genital armature, have been described in various Insects. See Burmeister, Man. of Entomology, p. 328 (Eng. Transl.); Siebold, Anat. of Invertebrates; Gosse in Linn. Trans., Ser. 2, Vol. II. (1883); Burgess on Milk-weed Butterfly, Ann. Mem. Bost. Soc. Nat. Hist.; &c.174In the following description it is to be understood that the observations have been made uponBlatta germanica, except whereP. orientalisis expressly named.175Fertilisation consists essentially in the union of an egg-nucleus (female nucleus) with a sperm-nucleus (male nucleus). From this union the first segmentation-nucleus is derived.176Balfour, Embryology, Vol. I., p. 337.177Q. J. Micr. Sci., Vol. XXIV., page 596 (1884).178Kowalewsky inHydrophilus, Graber inMuscaandLina, Patten inPhryganidæ, myself inMeloe, &c.179Biolog. Centrablatt. Bd. VI., No. 2 (1886).180These terms are explained on p.115.181Cf. Korotneff, Embryol. der Gryllotalpa. Zeits. f. wiss. Zool. (1885).182InGryllotalpa(Dohrn), as in Spiders, some Myriopods andPeripatus(Moseley, Phil. Trans., 1874), each stigma, with its branches, constitutes throughout life a separate system. The salivary glands arise in the same way, not, like the salivary glands of Vertebrates, as extensions of the alimentary canal, but as independent pits opening behind the mouth. Both the tracheal and the salivary passages are believed to be special modifications of cutaneous glands (Moseley).183Loc. cit.184This arrangement persists only inEphemeridæamong Insects (Palmen, Ueb. paarigen Ausführungsgänge der Geschlechtsorgane bei Insekten, 1884).185Genital pouch of the preceding description.186Indications, which we have not found time to work out, lead us to think that the development of the specially modified segments and appendages in the male and female Cockroach needs re-examination. We hope to treat this subject separately on a future occasion.—L. C. M. and A. D.187It may be useful to point out the following examples of parental care among animals in which, as a rule, the eggs are left to take care of themselves. It will be found that in general this instinct is associated with high zoological rank (best exemplified by Mammals and Birds), land or freshwater habitat, reduced number of eggs, and direct development.Amphibia.—The eggs are sometimes hatched by the male (Alytes obstetricans,Rhinoderma Darwinii), or placed by the male in pouches on the back of the female (Pipa dorsigera,Notodelphis ovifera,Nototrema marsupiatum), or carried during hatching by the female (Polypedates reticulatus).Fishes.—The Stickleback and others build nests. Of eleven genera of nest-building Fishes, eight are freshwater. The number of eggs is unusually small. Many Siluroids have the eggs hatched in the mouth of the males, a few under the belly of the female. The species are both marine and freshwater, the eggs few and large. Lophobranchiate fishes usually have the eggs hatched by the male. They are marine; the eggs few and large. Many sharks hatch their eggs, which are very few, within the body.Mustelus lævishas a placenta formed out of the yolk-sac.Insects.—De Geer has described the incubation of the Earwig, and the care of the brood by the female. The cases of the social Hymenoptera, &c., are universally known.Spiders.—The care of the female spider for her eggs is well known.Crustaceans.—The Crayfish hatches and subsequently protects her young.Mysis,Diastylis(Cuma), and some Isopods hatch their eggs.Gammarus locustais followed about by her brood, which shelter beneath her when alarmed.Podocerus capillatusbuilds a nest among corallines. Several of theCaprellidæhatch or otherwise protect their young. All these, except the Crayfish, are marine; the eggs commonly fewer than usual.Echinoderms.—Many cases of “marsupial development” have been recorded in the species of the Southern seas. Here development, contrary to the rule in Echinodermata, is direct.188The minute and early larvæ ofTœniaandDistomummay appear to contradict this statement. They really inhabit the film of water which spreads over wet grass, though they are capable of enduring dry conditions for a short time, like Rotifers and many Infusoria.189It is possible that the curious cases of agamogenetic reproduction of the larvæ ofAphis,Cecidomyia, andChironomusare vestiges of the original fertility of Insect larvæ.190“Alia vero semen adhuc imperfectum et immaturatum recludunt, incrementum et perfectionem, sive maturitatem, soris acquisiturum; ut plurima genera piscium, ranæ, item mollia, crustata, testacea, et cochleæ: quorum ova primum exposita sunt, veluti origines duntaxat, inceptiones et vitelli; qui postea albumina sibi ipsis circum circa induunt; tandemque alimentum sibi attrahentes, concoquentes et apponentes, in perfectum semen atque ovum evadunt. Talia sunt insectorum semina (vermes ab Aristotele dicta) quæ initio imperfecte edita sibi victum quærunt indeque nutriuntur et augentur, de eruca in aureliam; de ovo imperfecto in perfectum ovum et semen.”—De generatione, Exc. II., p. 183 (1666). Viallanes justifies this view by applying it to the histolysis and regeneration of the tissues in Diptera. But these remarkable changes are surely secondary, adaptive, and peculiar, like the footless maggot itself, whose conversion into a swift-flying imago renders necessary so complete a reconstruction.191The reader is recommended to refer to Fritz Müller’s Facts and Arguments for Darwin, especially chap. xi.; to Balfour’s Embryology, Vol. II., chap. xiii., sect. ii.; and to Lubbock’s Origin and Metamorphoses of Insects.192Those who care to see a bold experiment of this kind may refer to Haeckel’s Schöpfungsgeschichte.193Comp. Embryology, Vol. I., p. 451.194Yet none were so large as our largest living forms; their average size was very nearly that ofPeriplaneta americana.195Die Klassen und Ordnungen der Arthropoden. Leipzig, 8vo, p. 292.196A few elytra of Coleoptera are recently announced from the Silesian “culm.”197Memoirs Bost. Soc. Nat. Hist., III., 23 seq. (1880).198See a paper on mesozoic Cockroaches now printing in the Memoirs Bost. Soc. Nat. Hist., Vol. III., p. 439 seq.199The wingless creature from the Carboniferous deposits of Saarbrücken, described by Goldenberg as a Cockroach, under the name ofPolyzosterites granosus, appears to be a Crustacean.200This includes all possible forms; our table shows but nine.

1Baer’s account of Döllinger is to be found in the Leben und Schriften von K. E. von Baer, § 8.

2Prof. Plateau’s chief communications will be found on pp.131and159; Mr. Nusbaum has furnished the account of the Development of the Cockroach, pp.180to 195; and Mr. Scudder the Geological History of the Cockroach, chap. xi.

3Correspondence of John Ray, p.142.

4Copies dated 1762 have a plate representing the microscope and dissecting instruments used by the author.

5Dufour. Rech. anat. et phys. sur les Hémiptères (1833) les Orthoptères, les Hymenoptères et les Neuroptères (1841), et les Diptères (1851). Mém. de l’Institut, Tom. IV., VII., XI. Also many memoirs in Ann. des Sci. Nat.

6Newport. Art. “Insecta,” in Cycl. of Anat. and Phys. (1839), besides many special memoirs in the Phil. and Linn. Trans.

7Leydig. Vom Bau des Thierischen Körpers (1864), Tafeln zur vergl. Anatomie (1864), Untersuchungen zur Anat. und Histologie der Thiere (1883), &c., besides many special memoirs in Müller’s Archiv., Zeits. f. wiss. Zool., Nova Acta, &c.

8In some Insects there are traces of a fourth thoracic segment.

9So also in some larvæ (Calandra,Œstrus, &c.).

10In some aquatic Insects the exchange of gases is effected by “pseudobranchiæ,” and the tracheal system is closed.

11Dragon-flies have the male copulatory apparatus, but not the genital aperture, in the fore part of the abdomen.

12Aphis and Cecidomyia are at times viviparous, and a viviparous Moth has been observed by Fritz Müller (Trans. Entom. Soc. Lond., 1883).

13For descriptions of the species Fischer’s Orthoptera Europæa (1853) or Brunner von Wattenwyl’s Nouveau Système des Blattaires (1865) may be consulted. The classification adopted by the last-named author is here summarised.Blattariæ.A.—Femora spinous (Spinosæ).Fam. 1.—Ectobidæ.Seventh abdominal sternum undivided in female. Sub-anal styles absent in male. Wings with triangular apical area.Ectobia, includingE. lapponica(Blatta) and other genera.Fam. 2.—Phyllodromidæ.Seventh abdominal sternum undivided in female. Sub-anal styles usual in male (0 or rudimentary inPhyllodromia). Wings without triangular apical area.Phyllodromia, includingP. germanica(Blatta) and other genera.Fam. 3.—Epilampridæ.Fam. 4.—Periplanetidæ.Seventh abdominal sternum divided in female. Sub-anal styles conspicuous in male.Polyzosteria,Periplaneta, &c.B.—Femora not spinous (Muticæ).Families.—Chorisoneuridæ,Panchloridæ,Perisphæridæ,Corydidæ,Heterogamidæ,Blaberidæ,Panesthidæ.Many useful references will be found in Scudder’s Catalogue of N. American Orthoptera, Smiths. Misc. Coll., viii. (1868).

Blattariæ.

A.—Femora spinous (Spinosæ).

Fam. 1.—Ectobidæ.Seventh abdominal sternum undivided in female. Sub-anal styles absent in male. Wings with triangular apical area.Ectobia, includingE. lapponica(Blatta) and other genera.Fam. 2.—Phyllodromidæ.Seventh abdominal sternum undivided in female. Sub-anal styles usual in male (0 or rudimentary inPhyllodromia). Wings without triangular apical area.Phyllodromia, includingP. germanica(Blatta) and other genera.Fam. 3.—Epilampridæ.Fam. 4.—Periplanetidæ.Seventh abdominal sternum divided in female. Sub-anal styles conspicuous in male.Polyzosteria,Periplaneta, &c.

Fam. 1.—Ectobidæ.Seventh abdominal sternum undivided in female. Sub-anal styles absent in male. Wings with triangular apical area.Ectobia, includingE. lapponica(Blatta) and other genera.

Fam. 2.—Phyllodromidæ.Seventh abdominal sternum undivided in female. Sub-anal styles usual in male (0 or rudimentary inPhyllodromia). Wings without triangular apical area.Phyllodromia, includingP. germanica(Blatta) and other genera.

Fam. 3.—Epilampridæ.

Fam. 4.—Periplanetidæ.Seventh abdominal sternum divided in female. Sub-anal styles conspicuous in male.Polyzosteria,Periplaneta, &c.

B.—Femora not spinous (Muticæ).

Families.—Chorisoneuridæ,Panchloridæ,Perisphæridæ,Corydidæ,Heterogamidæ,Blaberidæ,Panesthidæ.

Many useful references will be found in Scudder’s Catalogue of N. American Orthoptera, Smiths. Misc. Coll., viii. (1868).

14Linnæus was certainly mistaken in his remark (Syst. Nat., 12th ed.) that this species is native to America, and introduced to the East—“Habitat in America: hospitatur in Oriente.” He adds, “Hodie in Russiæ adjacentibus regionibus frequens; incepit nuperis temporibus Holmiæ, 1739, uti dudum in Finlandia.”

15This must have been the “San Felipe,” a Spanish East Indiaman, taken in 1587. See Motley, United Netherlands, Vol. II., p. 283.

16Biblia Naturæ, Vol. I., p. 216.

17De Borck. Skandinaviens rätvingade Insekters Nat. Hist., I., i., 35.

18Brunner. N. Syst. d. Blattaires, p. 234.

19Scudder. Proc. Boston Soc. N.H., Vol. XIX., p. 94.

20For example, the Russians often call itProussaki, the Prussian Cockroach, and believe that their troops brought it home with them after the Seven Years’ War. The native Russian name isTarakan. In Finland and Sweden the same species is calledTorraka, which appears to be a corruption of the Russian word, and confirms the account of Linnæus quoted above.B. germanicais found in the United States from the Atlantic to the Pacific. It is generally known as the Croton Bug, because in New York it is often met with about the water pipes, which are supplied from the Croton River (Dr. Scudder).

B. germanicais found in the United States from the Atlantic to the Pacific. It is generally known as the Croton Bug, because in New York it is often met with about the water pipes, which are supplied from the Croton River (Dr. Scudder).

21Bell’s Edition, Vol. I., p. 454.

22British Museum Catalogue of Blattariæ (1868) and Supplement (1869). It is probable that the number is over-estimated in this catalogue, the same species being occasionally renamed.

23Brongniart has just described a Carboniferous Insect which he considers a Thysanuran (Dasyleptus Lucasi), though it has but one anal appendage. See C. R. Soc. Ent., France, 1885.

24Hummel, loc. cit.

25The use of the termpupato denote the last stage before the complete assumption of wings in the Cockroach, is liable to mislead. There is no resting-stage at all; wings are developed gradually, and are nearly as conspicuous in the last larval state as in the so-called pupa. There seems no reason for speaking of pupæ in this case.It is preferable to designate as “nymphs” young and active Insects, immature sexually, but with mouth-parts like those of the adult. See Lubbock, Linn. Trans., 1863, and Eaton, Linn. Trans., 1883.

It is preferable to designate as “nymphs” young and active Insects, immature sexually, but with mouth-parts like those of the adult. See Lubbock, Linn. Trans., 1863, and Eaton, Linn. Trans., 1883.

26SeeAppendix.

27Insectorum Theatrum, p. 138. The nameSchwabeis frequent in Franconia, where it is believed to have taken origin. Suabia adjoins Franconia, to the south.

28Compare the Swedish name (supra, p.18).

29A fuller list of vernacular names is given by Rolland, Faune Populaire de la France, Vol. III., p. 285. See also Nennich, Polyglotten Lexicon, Vol. I., p. 620.

30Anatomy of the Blow-fly, p.11.

31Q. J. Micr. Sci., 1871, p. 394.

32Krukenberg. Vergl. Physiologische Vorträge, p. 200. Halliburton, Q. J. Micr. Sci., 1885, p. 173.

33Ann. d. Chem. u. Pharm., Bd. 98.

34Previously observed by Leydig inCorethra.

35A condensed and popular account of these researches will be found in Semper’s Animal Life, p. 20.

36Prof. Huxley (Anat. Invert. Animals, p. 419) states that the integument splits along the abdomen also, but this is a mistake.

37Audouin. Rech. anat. sur le thorax des Insectes, &c. (Ann. Sci. Nat., Tom I., p. 97. 1824.)

38This application of the word to denote parts intermediate between terga and sterna has become general since its adoption by Audouin. It appears also in the older and deservedly obsolete nomenclature of Kirby and Spence. Professor Huxley has unfortunately disturbed the consistent use of this term by giving the namepleurato the free edges of the terga in Crustacea.

39Where the thorax apparently consists of four somites, as in some Hymenoptera, Hemiptera, Coleoptera, and Lepidoptera, the first abdominal segment has become blended with it.

40Balfour. Embryology, Vol. I., p. 337.

41E.g., by Graber. Insekten, Vol. II., p. 423.

42See, for example, Huxley on the Crayfish.

43One of the few points in which we have to differ from the admirable description of the Cockroach given in Huxley’s Comparative Anatomy of Invertebrated Animals, relates to the articulation of the mandible, which is there said to be carried by the gena.

44Morphologie des Tracheen-systems, p. 103.

45Zaddach, Entw. des Phryganiden Eies, p. 86; Rolleston, Forms of Animal Life, p. 75, &c.

46Zeits. f. wiss. Zool., Bd. XVI., pl. vii., fig. 33.

47Insekten, Vol. II., p. 508.

48Anat. Invert. Animals, p. 398.

49Professor Huxley has proposed to call the attached basehypopharynx, and the free tiplingua.

50Professor J. Wood-Mason points out that inMachilis(one of the Thysanura) the mandible shows signs of segmentation, while the apical portion is deeply divided into an inner and an outer half. Ripe embryos ofPanesthia (Blatta) javanicaare said to exhibit folds which indicate the consolidation of the mandible out of separate joints, while the cutting and crushing portions of the edge are divided by a “sutural mark,” which may correspond to the line of junction of the divisions of a biramous appendage (Trans. Ent. Soc., 1879, pt. 2, p. 145).

51The homology of the labium with the first pair of maxillæ is in no other Insects so distinct as in the Orthoptera.

52Rosenthal, Ueb. d. Geruchsinn der Insekten. Arch. f. Phys. Reil u. Autenrieth, Bd. X. (1811). Hauser, Zeits. f. wiss. Zool., Bd. XXXIV. (1880).

53Mém. Acad. Roy. de Belgique, Tom. XLI. (1874). Prof. Plateau’s writings will often be referred to in these pages. We owe to him the most important researches into the physiology of Invertebrates which have appeared for many years.

54Exp. sur le Rôle des Palpes chez les Arthropodes Maxillés. Pt. I. Bull. Soc. Zool. de France, Tom. X. (1885).

55Leydig, Taf. z. vergl. Anat., pl. x., fig. 3. Hauser, Zeits. f. wiss. Zool., Bd. XXXIV., p. 386. Jobert has figured the sensory organs of the maxillary palps of the Mole-cricket (Ann. Sci. Nat., 1872), and Forel similar organs in Ants (Bull. Soc. Vaudoise, 1885).

56The reader who desires to follow this subject further is recommended to study chap. vi. of Graber’s Insekten, which we have found very useful.

57Freshwater Crustacea, however, are sometimes similar to their parents at the time of hatching.

58InDytiscusthe mandibles are perforate at the base, and not at the tip. See Burgess in Proc. Bost. Soc. Nat. Hist., Vol. XXI., p. 223.

59Ein Käfer mit Schmetterlingsrüssel, Kosmos, Bd. VI. We take this reference from Hermann Müller’s Fertilisation of Flowers.

60An interesting account of the structure and mode of action of the Bee’s tongue is to be found in Hermann Müller’s Fertilisation of Flowers, where also the evolution of the parts is traced through a series of graduated types.

61See Newport’s figure of Vanessa atalanta (Todd’s Cyc., Art. Insecta), or Burgess on the Anatomy of the Milk-weed Butterfly, in Anniversary Mem. of Boston Soc. Nat. Hist., pl. ii., figs. 8–10 (1880).

62Balfour, Embryology, Vol. I., p. 337.

63Huxley, Med. Times and Gazette, 1856–7; Linn. Trans., Vol. XXII., p. 221, and pl. 38 (1858).

64“I think it is probable that these cervical sclerites represent the hindermost of the cephalic somites, while the band with which the maxillæ are united, and the genæ, are all that is left of the sides and roof of the first maxillary and the mandibular somites.”—Huxley, Anat. Invert. Animals, p. 403.

65Balfour, Embryology, Vol. I., note to p. 337.

66J. S. Kingsley in Q. J. Micr. Sci. (1885), has reviewed the homology of Insect, Arachnid, and Crustacean appendages, and comes to conclusions very different from those hitherto accepted. He classifies the appendages as pre-oral (Insect-antennæ) and post-oral, and makes the following comparisons:—Hexapoda.Acerata.Crustacea.(=Insecta + Myriopoda?)(=Arachnida + Limulus.)(1) Antennæ.Absent.Absent.(2) Mandibles.Cheliceræ.Antennules.(3) Maxillæ.Pedipalpi.Antennæ.(4) Labium.1st pair legs.Mandibles.(5) 1st pair legs.2nd pair legs.1st Maxillæ.(6) 2nd pair legs.3rd pair legs.2nd Maxillæ.(7) 3rd pair legs.4th pair legs.1st Maxillipeds.Pelseneer (Q. J. Micr. Sci., 1885), concludes that both pairs of antennæ are post-oral inApus, and probably in all other Crustacea.

Hexapoda.Acerata.Crustacea.(=Insecta + Myriopoda?)(=Arachnida + Limulus.)(1) Antennæ.Absent.Absent.(2) Mandibles.Cheliceræ.Antennules.(3) Maxillæ.Pedipalpi.Antennæ.(4) Labium.1st pair legs.Mandibles.(5) 1st pair legs.2nd pair legs.1st Maxillæ.(6) 2nd pair legs.3rd pair legs.2nd Maxillæ.(7) 3rd pair legs.4th pair legs.1st Maxillipeds.

Pelseneer (Q. J. Micr. Sci., 1885), concludes that both pairs of antennæ are post-oral inApus, and probably in all other Crustacea.

67Many Orthoptera, which seize their prey with the fore legs, have a very long pronotum.

68Also inPhasmidæ(see Scudder, Psyche, Vol. I., p. 137).

69Professor Huxley (Anat. Invert. Animals, p. 404) points out that the so-calledpulvillusought to be counted as a sixth joint. The same is true of the foot of Diptera and Hymenoptera, where there are six tarsal joints, the last carrying the claws. (Tuffen West on the Foot of the Fly. Linn. Trans., Vol. XXIII.)

70The nomenclature adopted by Packard (Third Report of U.S. Entomological Commission) seems to us open to theoretical objections.

71On wing-plaiting and wing-folding in Blattariæ see Saussure, Etudes sur l’aile des Orthoptères. Ann. Sci. Nat., Sér. 5e(Zool.), Tom. X.

72Grundzüge der Vergl. Anat. (Arthropoden, Athmungsorgane.)

73Origin and Metamorphoses of Insects, p. 73.

74Palmén cites one striking proof of the low position of Ephemeridæ among Insects. Their reproductive outlets are paired and separate, as in Worms and Crustacea.

75These examples are cited by Palmén.

76Eaton, Trans. Ent. Soc., 1868, p. 281; Vayssière, Ann. Sci. Nat., Zool., 1882, p. 91.

77Zur Morphologie des Tracheensystems (1877).

78We take these instances from Eaton, Monograph of Ephemeridæ, Linn. Trans., 1883, p. 15.

79Charles Brongniart has lately described a fossil Insect from the Coal Measures of Commentry, which he namesCorydaloides Scudderi, and refers to the Pseudo-Neuroptera. In this Insect every ring of the abdomen carries laminæ, upon which the ramified tracheæ can still be made out by the naked eye. Stigmata co-existed with these tracheal gills. (Bull. Soc. Sci. Nat. de Rouen, 1885.)Some Crustacea are furnished with respiratory leaflets, curiously like those of Tracheates, with which, however, they have no genetic connection. In Isopod Crustacea the exopodites of the anterior abdominal segments often form opercula, which protect the succeeding limbs. In the terrestrial Isopods,PorcellioandArmadillo, these opercula contain ramified air-tubes, which open externally, and much resemble tracheæ. The anterior abdominal appendages ofTylusare provided with air-chambers, each lodging brush-like bundles of air-tubes, which open to the outer air. Lamellæ, projecting inwards from the sides of the abdominal segments, incompletely cover in the hinder part of the ventral surface of the abdomen, and protect the modified appendages. (Milne Edwards, Hist. Nat. des Crustacés, Vol. III.)

Some Crustacea are furnished with respiratory leaflets, curiously like those of Tracheates, with which, however, they have no genetic connection. In Isopod Crustacea the exopodites of the anterior abdominal segments often form opercula, which protect the succeeding limbs. In the terrestrial Isopods,PorcellioandArmadillo, these opercula contain ramified air-tubes, which open externally, and much resemble tracheæ. The anterior abdominal appendages ofTylusare provided with air-chambers, each lodging brush-like bundles of air-tubes, which open to the outer air. Lamellæ, projecting inwards from the sides of the abdominal segments, incompletely cover in the hinder part of the ventral surface of the abdomen, and protect the modified appendages. (Milne Edwards, Hist. Nat. des Crustacés, Vol. III.)

80Gerstaecker has found in the two first abdominal segments ofCorydia carunculigera(Blattariæ) pleural appendages, which are hollow and capable of protrusion. They have no relation to the stigmata, which are present in the same segments, and their function is quite unknown. See Arch. f. Naturg., 1861, p. 107.

81Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera); in the Earwig they become modified and form the forceps. The “caudal filaments” ofApusare curiously like cerci.The cerci are concealed in the AmericanCryptocercus, Scudd. (Fam.Panesthidæ).

81Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera); in the Earwig they become modified and form the forceps. The “caudal filaments” ofApusare curiously like cerci.

The cerci are concealed in the AmericanCryptocercus, Scudd. (Fam.Panesthidæ).

82Entw. der Biene. Zeits. f. wiss. Zool. Bd. XX. Or, see Balfour’s Embryology, Vol. I., p. 338.

83From more recent observations it is probable that abdominal appendages are usually present in the embryos of Orthoptera, Coleoptera, Lepidoptera, and possibly Hymenoptera. The subject is rapidly advancing, and more will be known very shortly.

84See, for example, Klein’s Elements of Histology, chap. ix.

85The exceptions relate chiefly to the alary muscles of the pericardial septum. Lowne (Blow-fly, p. 5, and pl. v.) states that some of the thoracic muscles of that Insect are not striated.

86For example, Prof. Huxley, in his Anatomy of Invertebrated Animals (p. 254), says that “as the hard skeleton [of Arthropods] is hollow, and the muscles are inside it, it follows that the body, or a limb, is bent towards that side of its axis, which is opposite to that on which a contracting muscle is situated.” The flexor muscles of the tail of the Crayfish, which, according to the above rule, should be extensors, the muscles of the mandibles of an Insect, and the flexors and extensors of Crustacean pincers are among the many conspicuous exceptions to this rule.

87Haller. This and other examples are taken from Rennie’s Insect Transformations.

88Bull. Acad. Roy. de Belgique, 2e.Sér., Tom. xx. (1865), and Tom. xxii. (1866).

89Loc. cit. 3e.Sér., Tom. vii. (1884). Authorities for the various estimates are cited in the original memoir.

90Klassen und Ordnungen des Thierreichs, Bd. V., pp. 61–2.

91This change in the relation of weight to strength, according to the size of the structure, has long been familiar to engineers. (See, for example, “Comparisons of Similar Structures as to Elasticity, Strength, and Stability,” by Prof. James Thomson, Trans. Inst. Engineers, &c., Scotland, 1876.) The application to animal structures has been made by Herbert Spencer (Principles of Biology, Pt. II., ch. i.). The principle can be readily explained by models. Place a cubical block upon a square column. Double all the dimensions in a second model, which may be done by fitting together eight cubes like the first, and four columns, also the same as before except in length. Each column, though no stronger than before, has now to bear twice the weight.

92Contractile force varies as sectional area of muscle. LetWbe weight of Horse;w, weight of Bee;R, a linear dimension of Horse;r, a linear dimension of Bee. Then,Contr. force of Hors eContr. force of Bee=sect. area of muscles (Horse )sect. area of muscles (Bee)=R2r2.But sinceWw=R3r3,R2r2=Ww×rR.ThereforeContr. force of HorseContr. force of Bee=WrwRBut, by definition,Rel. m.f. of HorseRel. m.f. of Bee=Contr. f. of HorseWContr. f. of Beew=Contr. f. of HorseContr. f. of Bee×wW=WrwR×wW=rR=r3R313=wW13.The weight of a horse is about 270,000 grammes, that of a bee ·09 gramme; so thatwW13=·09270,00013=·000,000,3̅13= ·0015 (nearly) =Calculated Ratio of Relative Muscular Force of Horse to that of Bee. The Observed Ratio (Plateau) is·523·5= ·02128; so that the relative muscular force of the Horse is more than fourteen times as great in comparison with that of the Bee as it would be if the muscles of both animals were similar in kind, and the proportions of the two animals similar in all respects.

92Contractile force varies as sectional area of muscle. LetWbe weight of Horse;w, weight of Bee;R, a linear dimension of Horse;r, a linear dimension of Bee. Then,

Contr. force of Hors eContr. force of Bee=sect. area of muscles (Horse )sect. area of muscles (Bee)=R2r2.

But sinceWw=R3r3,R2r2=Ww×rR.

ThereforeContr. force of HorseContr. force of Bee=WrwR

But, by definition,

Rel. m.f. of HorseRel. m.f. of Bee=Contr. f. of HorseWContr. f. of Beew=Contr. f. of HorseContr. f. of Bee×wW=

WrwR×wW=rR=r3R313=wW13.

The weight of a horse is about 270,000 grammes, that of a bee ·09 gramme; so that

wW13=·09270,00013=·000,000,3̅13= ·0015 (nearly) =

Calculated Ratio of Relative Muscular Force of Horse to that of Bee. The Observed Ratio (Plateau) is·523·5= ·02128; so that the relative muscular force of the Horse is more than fourteen times as great in comparison with that of the Bee as it would be if the muscles of both animals were similar in kind, and the proportions of the two animals similar in all respects.

93Rech. sur la Force Absolue des Muscles des Invertébrés. IePartie. Mollusques Lamellibranches. Bull. Acad. Roy. de Belgique, 3eSér., Tom. VI. (1883).Do., IIePartie. Crustacés Décapodes. Ibid., Tom. VII. (1884).

93Rech. sur la Force Absolue des Muscles des Invertébrés. IePartie. Mollusques Lamellibranches. Bull. Acad. Roy. de Belgique, 3eSér., Tom. VI. (1883).

Do., IIePartie. Crustacés Décapodes. Ibid., Tom. VII. (1884).

94Statical muscular forceandSpecific muscular forceare synonymous terms in common use.Contractile force per unit of sectional areagives perhaps the clearest idea of what is meant.

95Vol. II., p. 203. The calculation here quoted is based upon an observation of Swammerdam, who relates that a Cheese-hopper,1/4in. long, leaped out of a box 6 in. deep.

96Haughton’s Animal Mechanics, 2nd ed., p. 43.

97In any comparison it is necessary to cite not the height cleared by the man, but the displacement during the leap of his centre of gravity.

98The granules are not shown in the figure, having been removed in the preparation of the tissue for microscopic examination.

99Balfour, Embryology, Vol. II., p. 603.

100Yung (“Syst. nerveux des Crustacées Décapodes, Arch. de Zool. exp. et gén.,” Tom. VII., 1878) proposes to nameconnectivesthe longitudinal bundles of nerve-fibres which unite the ganglia, and to reserve the termcommissuresfor the transverse communicating branches.

101This commissure, which has been erroneously regarded as characteristic of Crustacea, was found by Lyonnet in the larva of Cossus, by Straus-Dürckheim in Locusta and Buprestis, by Blanchard in Dytiscus and Otiorhynchus, by Leydig in Glomeris and Telephorus, by Dietl in Gryllotalpa, and by Liénard in a large number of other Insects and Myriapods, including Periplaneta. See Liénard, “Const. de l’anneau œsophagien,” Bull. Acad. Boy. de Belgique, 2eSér., Tom. XLIX., 1880.

102We have not been able to distinguish in the adult Cockroach thedoublelayer of neurilemmar cells noticed by Leydig and Michels in various Coleoptera.

103Traité Anat., p. 201, pl. ix., fig. 1.

104Phil. Trans., 1834, p. 401, pl. xvi.

105Vom Bau des Thierischen Körpers, pp. 203, 262; Taf. z. vergl. Anat., pl. vi., fig. 3.

106The stomato-gastric nerves of the Cockroach have been carefully described by Koestler (Zeits. f. wiss. Zool., Bd. XXXIX., p. 592).

107“Mem. Acad. Petersb.,” 1835.

108“Q. J. Micr. Sci.,” 1879, pp. 340–350, pl. xv., xvi.

109“Journ. Quekett Micr. Club,” 1879.

110It is to be remarked that unusually large nerves supply the cerci of the Cockroach.

111The number in Insects varies from eight to four, but seven is usual; four is the usual number in Crustacea.

112“Q. J. Micr. Sci.,” 1885.

113Exner has since determined by measurement and calculation the optical properties of the eye of Hydrophilus. He finds that the focus of a corneal lens is about 3mm. away, and altogether behind the eye.

114Zur vergl. Phys. des Gesichtsinnes.

115A critical history of the whole discussion is to be found in Grenacher’s “Sehorgan der Arthropoden” (1879), from which we take many historical and structural details.

116Flies, whose eyes are in several respects exceptional, have almost completely separated rods, notwithstanding their quick sight.

117Bull. de l’Acad. Roy. de Belgique, 1885.

118References to the literature of the question are given by Hauser in Zeits. f. wiss. Zool., Bd. XXXIV., and by Plateau in Bull. Soc. Zool. de France, Tom. X.

119Zeits. f. wiss. Zool., 1885.

120Will confirms, by his own experiments (p. 685), Plateau’s conclusion (Supra, p.46), that the maxillary and labial palps have nothing to do with the choice of food.

121For a popular account of auditory organs in Insects, see Graber’s Insekten, Vol. I., page 287; also J. Müller, Vergl. Phys. d. Gesichssinn, p. 439; Siebold, Arch. f. Naturg., 1844; Leydig, Müller’s Arch. 1855 and 1860; Hensen, Zeits. f. wiss. Zool., 1866; Graber, Denkschr. der Akad. der wiss. Wien, 1875; and Schmidt, Arch. f. mikr. Anat., 1875.

122Here, as generally in the digestive tube of the adult Cockroach, the peritoneal layer is inconspicuous or wanting. It occasionally becomes visible—e.g., in the outer wall of the Malpighian tubules, and in the tubular prolongation of the gizzard.

123Plateau has expressed a strong opinion that neither in the stomach of Crustacea nor in the gizzard of Insects have the so-called teeth any masticatory character. He compares them to the psalterium of a Ruminant, and considers them strainers and not dividers of the food. His views, as stated by himself, will be found on p.131.

124See Watney, Phil. Trans., 1877, Pt. II. The “epithelial buds” described and figured in this memoir are also closely paralleled in the chylific stomach of the Cockroach.

125These epithelial buds have been described as glands, and we only saw their significance after comparing them with Dr. Watney’s account.

126Development shows that these tubules belong to the proctodæum, and not to the mesenteron.

127The epithelial bands of the rectum of Insects were first discovered by Swammerdam in the Bee (Bibl. Nat., p. 455, pl. xviii., fig. 1). Dufour called them muscular bands (Rech. sur les Orthoptères, &c., p. 369, fig. 44).

128“Lehrbuch der Histologie,” p. 337.

129Except in Dragon-flies and Ephemeræ.

130Zeitsch. f. wiss. Zool., Bd. XXX.

131The contents of the Malpighian tubules may be examined by crushing the part in a drop of dilute acetic acid, or in dilute sulphuric acid (10 per cent.). In the first case a cover-slip is placed on the fluid, and the crystals, which consist of oblique rhombohedrons, or derived forms, are usually at once apparent. If sulphuric acid is used, the fluid must be allowed to evaporate. In this case they are much more elongated, and usually clustered. The murexide reaction does not give satisfactory indications with the tubules of the Cockroach.

132Bull. Acad. Roy. de Belgique, 1876.

133Ib., 1877.

134We are indebted to Prof. Plateau for the statement of his views given in the text.

135Dissert. de Bombyce, pp. 15, 16 (1669).

136Biblia Naturæ, p. 410.

137Schrift. d. Marburg. Naturf. Gesellschaft, 1823.

138See, for a full account of this discussion, MacLeod sur la Structure des Trachées, et la Circulation Péritrachéenne (1880). The peritracheal circulation was refuted by Joly (Ann. Sci. Nat., 1849).

139It may be observed that Graber, who has paid close attention to the heart of Insects, describes the inlets (e. g., inDytiscus) as situated, not at the hinder end, but in the middle of each segment. We have not been able to discover such an arrangement in the heart of the Cockroach.

140Lyonnet.

141Brandt, Ueb. d. Herz der Insekten u. Muscheln. Mél. Biol. Bull. Acad. St. Petersb. Tom. VI. (1866).

142Arch. f. mikr. Anat., Bd. IX. (1872); Insekten, ch. x.

143Newport, in Todd’s Cyclopædia of Anatomy and Physiology, Art. Insecta, pp. 981–2.

144Beitr. zur näheren Kenntniss von Periplaneta orientalis, p. 19.

145The termination of the aorta has been described by Newport, inSphinx(Phil. Trans., 1832, Pt. I., p. 385)Vanessa, Meloe, Blaps and Timarcha. (Todd’s Cycl., Art. “Insecta,” p. 978.)

146Moseley, Q. J. Micr. Sci. (1871).

147The oldest Tracheate actually known to bear spiracles is the Silurian Scorpion of Gothland and Scotland (Scudder, in Zittel’s Palæontologie, p. 738). We need not say that this is very far removed from the primitive Tracheate which morphological theory requires. The existingPeripatusmakes a nearer approach to the ideal ancestor of all Tracheates, if we suppose that all Tracheates had a common ancestor of any kind, which is not as yet beyond doubt.

148The longitudinal air-tubes are characteristic of the more specialised Tracheata. In Araneidæ, many Julidæ, and Peripatus each spiracle has a separate tracheal system of its own.

149Investigators are not yet agreed as to the minute structure of the tracheal thread. Chun (Abh. d. Senkenberg. Naturf. Gesells., Bd. X., 1876) considers it an independent chitinous formation, not a mere thickening of the intima. He describes the thread as solid. The intima itself is, he believes, divisible in the larger tubes into an inner and an outer layer, into both of which the thread is sunk. Macloskie (Amer. Nat., June, 1884) describes the spiral as a fine tubule, opening by a fissure along its length. He regards it as a hollow crenulation of the intima, and continuous therewith. Packard (Amer. Nat. Mag., May, 1886) endeavours to show that the thread is not spiral, but consists of parallel thickenings of the intima. He is unable to find proof of the tubular structure, or of the external fissure. We have specially examined the trachea of the Cockroach, and find that the thread can readily be unwound for several turns. It is truly spiral.

150It has been supposed that these irregular cells of the tracheal endings pass into those of the fat-body, but the latter can always be distinguished by their larger and more spherical nuclei.

151In the first abdominal spiracle the setæ are developed only on that lip which carries the bow.

152This subject is treated at greater length in Prof. Plateau’s contribution on Respiratory Movements of Insects. (Infra, p.159.)

153Phil. Mag., 1833. Reprinted in “Researches,” p. 44. Graham expressly applies the law of diffusion of gases to explain the respiration of Insects. Sir John Lubbock quotes and comments upon the passage in his paper on the Distribution of the Tracheæ in Insects. (Linn. Trans. Vol. XXIII.)

154For an explanation of the physical principles involved in this discussion, and for the calculation (based upon our own assumptions), we are indebted to Mr. A. W. Rücker, F.R.S.

155J. Hutchinson, Art. Thorax, Todd’s Cycl. of Anat. and Phys.

156De l’absence de mouvements respiratoires perceptibles chez les Arachnides (Archives de Biologie de Van Beneden et Van Bambeke, 1885.)

157Ueb. d. Respiration der Tracheaten. Chemnitz (1872).

158See table in Burmeister’s “Manual,” Eng. trans. p. 398.

159Art. “Insecta,” Cyc. Anat. and Phys., p. 989.

160Pogg. Ann. 1872, Hft. 3.

161Works, Vol. IX., p. 287. This passage has been cited by Rathke.

162Arbeiten a. d. Zool. Zoot. Inst. Würzburg. Bd. II., 1874.

163Phil. Trans., 1874, p. 757.

164The crystals have been supposed to consist of oxalate of lime (Duchamp, Rev. des sci. nat. Montpellier, Tom. VIII.). Hallez observes that they are prismatic, with rhombic base, the angles truncated. They are insoluble in water and weak nitric acid, but dissolve rapidly in strong sulphuric acid without liberation of gas, and still more rapidly in caustic potash. (Compt. Rend., Aug., 1885.)

165It is usually stated that the spermatheca of the Cockroach opens into the uterus, as it does in most other Insects, but this is not true. Locusts and Grasshoppers have the outlet of the spermatheca placed as in the Cockroach; in other European Orthoptera, it lies upon the dorsal wall of the uterus. (Berlese, loc. cit., p. 273.)

166It is a striking proof of the sagacity of Malpighi, that he should have observed in the Silkworm the spermatophore of the male (“in spiram circumvolutum persimile semen”) and the spermatheca of the female. His reasoning as to the function of the spermatheca wanted nothing but microscopic evidence of the actual transference of spermatozoa to establish it in all points. Audouin and Siebold supplied what was wanting nearly two centuries later, but they mistook the spirally wound spermatophore for a broken-off penis, and Stein (Weibl. Geschlechtsorgane der Käfer, p. 85) first arrived at the complete proof of Malpighi’s explanation.

167The descriptions and figures of the reproductive appendages of female Orthoptera by Lacaze-Duthiers (Ann. Sci. Nat., 1852) are so often consulted, that it may be useful to explain how we understand and name the same parts. In pl. xi., fig. 2, 8′ and 9′ are the 8th and 9th terga; the anterior gonapophyses are seen to be attached to them below;a(figs. 2 and 4) is the base of the same appendage, but the twisted ends are incorrect; the 8th sternum is seen at the back (figs. 2 and 4);a′ represents the outer,fthe inner pair of posterior gonapophyses.

168We propose to notice here the chief differences which we have found between the figures of Brehm (loc. cit.), which are the fullest and best we have seen, and our own dissections.Figs. 10, 11 (pp. 169–70). The ejaculatory duct and duct of the conglobate gland are made to end in the penis (infra, p. 178).Figs. 14, 15 (p. 173). These figures seem to us erroneous in many respects, such as the median position of the penis and titillator.Fig. 16 (p. 174). The pair of hooks markedEare too small, and there are additional plates at the base, which are not figured (see our fig.102).F(of our fig.) is omitted.

168We propose to notice here the chief differences which we have found between the figures of Brehm (loc. cit.), which are the fullest and best we have seen, and our own dissections.

Figs. 10, 11 (pp. 169–70). The ejaculatory duct and duct of the conglobate gland are made to end in the penis (infra, p. 178).

Figs. 14, 15 (p. 173). These figures seem to us erroneous in many respects, such as the median position of the penis and titillator.

Fig. 16 (p. 174). The pair of hooks markedEare too small, and there are additional plates at the base, which are not figured (see our fig.102).F(of our fig.) is omitted.

169InBlatta germanicathe testes are functional throughout life. They consist of four lobes each. The vasa deferentia are much shorter than inP. orientalis.

170The spermatocysts are peculiar to Insects and Amphibia. They arise by division of the spermatospores, or modified epithelial cells, and form hollow cysts, within which sperm cells (or spermatoblasts) are developed by further division. The sperm cells are usually placed radiately around the wall of the spermatocyst. They escape by dehiscence, and are transformed into spermatozoa.

171Huxley, Anat. Invert. Animals, p. 416.

172The term “accessory gland,” used by Huxley and others, is already appropriated to glands which we believe to be represented by the utricles of the Cockroach, and which have only a general correspondence with the gland in question.

173Similar organs, forming a male genital armature, have been described in various Insects. See Burmeister, Man. of Entomology, p. 328 (Eng. Transl.); Siebold, Anat. of Invertebrates; Gosse in Linn. Trans., Ser. 2, Vol. II. (1883); Burgess on Milk-weed Butterfly, Ann. Mem. Bost. Soc. Nat. Hist.; &c.

174In the following description it is to be understood that the observations have been made uponBlatta germanica, except whereP. orientalisis expressly named.

175Fertilisation consists essentially in the union of an egg-nucleus (female nucleus) with a sperm-nucleus (male nucleus). From this union the first segmentation-nucleus is derived.

176Balfour, Embryology, Vol. I., p. 337.

177Q. J. Micr. Sci., Vol. XXIV., page 596 (1884).

178Kowalewsky inHydrophilus, Graber inMuscaandLina, Patten inPhryganidæ, myself inMeloe, &c.

179Biolog. Centrablatt. Bd. VI., No. 2 (1886).

180These terms are explained on p.115.

181Cf. Korotneff, Embryol. der Gryllotalpa. Zeits. f. wiss. Zool. (1885).

182InGryllotalpa(Dohrn), as in Spiders, some Myriopods andPeripatus(Moseley, Phil. Trans., 1874), each stigma, with its branches, constitutes throughout life a separate system. The salivary glands arise in the same way, not, like the salivary glands of Vertebrates, as extensions of the alimentary canal, but as independent pits opening behind the mouth. Both the tracheal and the salivary passages are believed to be special modifications of cutaneous glands (Moseley).

183Loc. cit.

184This arrangement persists only inEphemeridæamong Insects (Palmen, Ueb. paarigen Ausführungsgänge der Geschlechtsorgane bei Insekten, 1884).

185Genital pouch of the preceding description.

186Indications, which we have not found time to work out, lead us to think that the development of the specially modified segments and appendages in the male and female Cockroach needs re-examination. We hope to treat this subject separately on a future occasion.—L. C. M. and A. D.

187It may be useful to point out the following examples of parental care among animals in which, as a rule, the eggs are left to take care of themselves. It will be found that in general this instinct is associated with high zoological rank (best exemplified by Mammals and Birds), land or freshwater habitat, reduced number of eggs, and direct development.Amphibia.—The eggs are sometimes hatched by the male (Alytes obstetricans,Rhinoderma Darwinii), or placed by the male in pouches on the back of the female (Pipa dorsigera,Notodelphis ovifera,Nototrema marsupiatum), or carried during hatching by the female (Polypedates reticulatus).Fishes.—The Stickleback and others build nests. Of eleven genera of nest-building Fishes, eight are freshwater. The number of eggs is unusually small. Many Siluroids have the eggs hatched in the mouth of the males, a few under the belly of the female. The species are both marine and freshwater, the eggs few and large. Lophobranchiate fishes usually have the eggs hatched by the male. They are marine; the eggs few and large. Many sharks hatch their eggs, which are very few, within the body.Mustelus lævishas a placenta formed out of the yolk-sac.Insects.—De Geer has described the incubation of the Earwig, and the care of the brood by the female. The cases of the social Hymenoptera, &c., are universally known.Spiders.—The care of the female spider for her eggs is well known.Crustaceans.—The Crayfish hatches and subsequently protects her young.Mysis,Diastylis(Cuma), and some Isopods hatch their eggs.Gammarus locustais followed about by her brood, which shelter beneath her when alarmed.Podocerus capillatusbuilds a nest among corallines. Several of theCaprellidæhatch or otherwise protect their young. All these, except the Crayfish, are marine; the eggs commonly fewer than usual.Echinoderms.—Many cases of “marsupial development” have been recorded in the species of the Southern seas. Here development, contrary to the rule in Echinodermata, is direct.

Amphibia.—The eggs are sometimes hatched by the male (Alytes obstetricans,Rhinoderma Darwinii), or placed by the male in pouches on the back of the female (Pipa dorsigera,Notodelphis ovifera,Nototrema marsupiatum), or carried during hatching by the female (Polypedates reticulatus).Fishes.—The Stickleback and others build nests. Of eleven genera of nest-building Fishes, eight are freshwater. The number of eggs is unusually small. Many Siluroids have the eggs hatched in the mouth of the males, a few under the belly of the female. The species are both marine and freshwater, the eggs few and large. Lophobranchiate fishes usually have the eggs hatched by the male. They are marine; the eggs few and large. Many sharks hatch their eggs, which are very few, within the body.Mustelus lævishas a placenta formed out of the yolk-sac.Insects.—De Geer has described the incubation of the Earwig, and the care of the brood by the female. The cases of the social Hymenoptera, &c., are universally known.Spiders.—The care of the female spider for her eggs is well known.Crustaceans.—The Crayfish hatches and subsequently protects her young.Mysis,Diastylis(Cuma), and some Isopods hatch their eggs.Gammarus locustais followed about by her brood, which shelter beneath her when alarmed.Podocerus capillatusbuilds a nest among corallines. Several of theCaprellidæhatch or otherwise protect their young. All these, except the Crayfish, are marine; the eggs commonly fewer than usual.Echinoderms.—Many cases of “marsupial development” have been recorded in the species of the Southern seas. Here development, contrary to the rule in Echinodermata, is direct.

Fishes.—The Stickleback and others build nests. Of eleven genera of nest-building Fishes, eight are freshwater. The number of eggs is unusually small. Many Siluroids have the eggs hatched in the mouth of the males, a few under the belly of the female. The species are both marine and freshwater, the eggs few and large. Lophobranchiate fishes usually have the eggs hatched by the male. They are marine; the eggs few and large. Many sharks hatch their eggs, which are very few, within the body.Mustelus lævishas a placenta formed out of the yolk-sac.

Insects.—De Geer has described the incubation of the Earwig, and the care of the brood by the female. The cases of the social Hymenoptera, &c., are universally known.

Spiders.—The care of the female spider for her eggs is well known.

Crustaceans.—The Crayfish hatches and subsequently protects her young.Mysis,Diastylis(Cuma), and some Isopods hatch their eggs.Gammarus locustais followed about by her brood, which shelter beneath her when alarmed.Podocerus capillatusbuilds a nest among corallines. Several of theCaprellidæhatch or otherwise protect their young. All these, except the Crayfish, are marine; the eggs commonly fewer than usual.

Echinoderms.—Many cases of “marsupial development” have been recorded in the species of the Southern seas. Here development, contrary to the rule in Echinodermata, is direct.

188The minute and early larvæ ofTœniaandDistomummay appear to contradict this statement. They really inhabit the film of water which spreads over wet grass, though they are capable of enduring dry conditions for a short time, like Rotifers and many Infusoria.

189It is possible that the curious cases of agamogenetic reproduction of the larvæ ofAphis,Cecidomyia, andChironomusare vestiges of the original fertility of Insect larvæ.

190“Alia vero semen adhuc imperfectum et immaturatum recludunt, incrementum et perfectionem, sive maturitatem, soris acquisiturum; ut plurima genera piscium, ranæ, item mollia, crustata, testacea, et cochleæ: quorum ova primum exposita sunt, veluti origines duntaxat, inceptiones et vitelli; qui postea albumina sibi ipsis circum circa induunt; tandemque alimentum sibi attrahentes, concoquentes et apponentes, in perfectum semen atque ovum evadunt. Talia sunt insectorum semina (vermes ab Aristotele dicta) quæ initio imperfecte edita sibi victum quærunt indeque nutriuntur et augentur, de eruca in aureliam; de ovo imperfecto in perfectum ovum et semen.”—De generatione, Exc. II., p. 183 (1666). Viallanes justifies this view by applying it to the histolysis and regeneration of the tissues in Diptera. But these remarkable changes are surely secondary, adaptive, and peculiar, like the footless maggot itself, whose conversion into a swift-flying imago renders necessary so complete a reconstruction.

191The reader is recommended to refer to Fritz Müller’s Facts and Arguments for Darwin, especially chap. xi.; to Balfour’s Embryology, Vol. II., chap. xiii., sect. ii.; and to Lubbock’s Origin and Metamorphoses of Insects.

192Those who care to see a bold experiment of this kind may refer to Haeckel’s Schöpfungsgeschichte.

193Comp. Embryology, Vol. I., p. 451.

194Yet none were so large as our largest living forms; their average size was very nearly that ofPeriplaneta americana.

195Die Klassen und Ordnungen der Arthropoden. Leipzig, 8vo, p. 292.

196A few elytra of Coleoptera are recently announced from the Silesian “culm.”

197Memoirs Bost. Soc. Nat. Hist., III., 23 seq. (1880).

198See a paper on mesozoic Cockroaches now printing in the Memoirs Bost. Soc. Nat. Hist., Vol. III., p. 439 seq.

199The wingless creature from the Carboniferous deposits of Saarbrücken, described by Goldenberg as a Cockroach, under the name ofPolyzosterites granosus, appears to be a Crustacean.

200This includes all possible forms; our table shows but nine.

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