Chapter 22

Family—Phrynichidae (Phrynichus,Damon).”   Admetidae (Admetus,Heterophrynus).”   Charontidae (Charon,Sarax).(Family ?)—*Graeophonus.Fig.59.—Schizomus crassicaudatus, one of the Pedipalpi. Lateral view of a male. II to VI, the prosomatic appendages, the first being concealed (see fig. 58); 5, the fifth, and 11, the eleventh tergites of the opisthosoma;pa, the conical post-anal lobe.(Original as preceding.)Remarks.—The Pedipalpi are confined to the tropics and warmer temperate regions of both hemispheres. Fossil forms occur in the Carboniferous. The small forms known asSchizomusandHubbardiaare of special interest from a morphological point of view. The Pedipalpi have no poison glands. (Reference to literature (29).)Fig.60.—Liphistius desultor, Schiödte, one of the Araneae Mesothelae. Dorsal view. I to VI, the prosomatic appendages; 4, 5, 6, the fourth, fifth and sixth tergites of the opisthosoma. Between the bases of the sixth pair of limbs and behind the prosomatic carapace is seen the tergite of the small prae-genital somite.(Original by Pickard-Cambridge and Pocock.)Order 3. Araneae(figs. 60 to 64.).—Prosoma covered with a single shield and typically furnished with median and lateral eyes of diplostichous structure, as in the Amblypygi. The sternal surface wide, continuously chitinized, but with prosternal and metasternal elements generally distinguishable at the anterior and posterior ends respectively of the large mesosternurm. Prosternum underlying the proboscis. Appendages of 1st pair have two segments, as in Pedipalpi, but are furnished with poison gland, and are retroverts. Appendages of 2nd pair not underlying the mouth, but freely movable and, except in primitive forms, furnished with a maxillary lobe; the rest of the limb like the legs, tipped with a single claw and quite unmodified (except in ♂). Remaining pairs of appendages similar in form and function, each tipped with two or three claws. Opisthosoma when segmented showing the same number of somites as in the Pedipalpi; usually unsegmented, the prae-genital somite constricted to form the waist; the appendages of its 3rd and 4th somites retained as spinning mammillae. Respiratory organs (see fig. 63,stg), as in the Amblypygi, or with the posterior pair, rarely the anterior pair as well, replaced by tracheal tubes. Intromittent organ of male in the apical segment of the 2nd prosomatic appendage.Fig.61.—Liphistius desultor. Ventral view with the prosomatic appendages cut short excepting the chelicerae (1) whose sharp retroverts are seen. Between the bases of the prosomatic limbs an anterior and a posterior sternal plate (black) are seen. 1, The sternum of the first opisthosomatic or genital somite covering the genital aperture and the first pair of lung-sacs. In front of it the narrow waist is formed by the soft sternal area of the praegenital somite; 2, the sternite of the second opisthosomatic somite covering the posterior pair of lung-sacs; 3 and 4, the spinning appendages (limbs) of the opisthosoma;a, inner,b, outer ramus of the appendage; 11, sternite of the eleventh somite of the opisthosoma: in front of it other rudimentary sternites;an, anus.(Original as above.)Sub-ordera. Mesothelae (see figs. 60 to 62).—Opisthosoma distinctly segmented, furnished with 11 tergal plates, as in the Amblypygi; the ventral surface of the 1st and 2nd somites with large sternal plates, covering the genital aperture and the two pairs of pulmonary sacs, the sternal plates from the 6th to the 11th somites represented by integumental ridges, weakly chitinized in the middle. The two pairs of spinning appendages retain their primitive position in the middle of the lower surface of the opisthosoma far in advance of the anus on the 3rd and 4th somites, each appendage consisting of a stout, many-jointed outer branch and a slender, unsegmented inner branch. Prosoma as in the Mygalomorphae, except that the mesosternal area is long and narrow.Family—Liphistiidae (Liphistius, *Arthrolycosa).Sub-orderb. Opisthothelae (see fig. 63).—Opisthosoma without trace of separate terga and sterna, the segmentation merely represented posteriorly by slight integumental folds and the sterna of the 1st and 2nd somites by the opercular plates of the pulmonary sacs. The spinning appendages migrate to the posterior end of the opisthosoma and take up a position close to the anus; the inner branches of the anterior pair either atrophy or are represented homogenetically by a plate, the cribellum, or by an undivided membranous lobe, the colulus.Fig.62.—Liphistius desultor. Lateral view.I to VI, Appendages of the prosoma cut off at the base.o, Ocular tubercle.prae-gen, The prae-genital somite.1 and 2, Sternites of the first and second opisthosomatic somites.3 and 4, Appendages of the third and fourth opisthosomatic somites, which are the spinning organs, and in this genus occupy their primitive position instead of migrating to the anal region as in other spiders.5, Tergite of the fifth opisthosomatic somite.11, Eleventh opisthosomatic somite;an, Anus.(Original.)Tribe 1. Mygalomorphae.—The plane of the articulation of the appendages of the 1st pair to the prosoma (the retrovert) vertical, the basal segment projecting straight forwards at its proximal end, the distal segment or fang closing backwards in a direction subparallel to the long axis of the body. Two pairs of pulmonary sacs.Families—Theraphosidae (Avicularia,Poecilotheria). Barychelidae (Barychelus,Plagiobothrus). Dipluridae (Diplura,Macrothele). Ctenizidae (Cteniza,Nemesia). Atypidae (Atypus,Calommata).Tribe 2. Arachnomorpnae.—The plane of the articulation of the appendages of the 1st pair to the prosoma horizontal, the basal segment projecting vertically downwards, at least at its proximal end, the distal segment or fang closing inwards nearly or quite at right angles to the long axis of the body. The posterior pulmonary sacs (except inHypochilus) replaced by tracheal tubes; the anterior and posterior pairs replaced by tracheal tubes in the Caponiidae.Principal families—Hypochilidae (Hypochilus). Dysderidae (Dysdera,Segestria). Caponiidae (Caponia,Nops). Filistatidae (Filistata). Uloboridae (Uloborus,Dinopis). Argiapidae (Nephila,Gasteracantha). Pholcidae (Pholcus,Artema). Agelenidae (Tegenuria). Lycosidae (Lycosa). Clubionidae (Clubiona,Olios,Sparassus) Gnaphosidae (Gnaphosa,Hemiclaea). Thomisidae (Thomisus). Attidae (Salticus). Urocteidae (Uroctea). Eresidae (Eresus).Remarks on the Araneae.—The Spiders are the most numerousand diversified group of the Arachnida; about 2000 species are known. No noteworthy fossil spiders are known; the best-preserved are in amber of Oligocene age.ProtolycosaandArthrolycosaoccur in the Carboniferous. Morphologically, the spiders are remarkable for the concentration and specialization of their structure, which is accompanied with high physiological efficiency. The larger species of Bird’s Nest Spiders (Avicularia), the opisthosoma of which is as large as a bantam’s egg, undoubtedly attack young birds, and M’Cook gives an account of the capture in its web by an ordinary house spider of a small mouse. The “retrovert” or bent-back first pair of appendages is provided with a poison gland opening on the fang or terminal segment. Spiders form at least two kinds of constructions—snares for the capture of prey and nests for the preservation of the young. The latter are only formed by the female, which is a larger and more powerful animal than the male. Like the scorpions the spiders have a special tendency to cannibalism, and accordingly the male, in approaching the female for the purpose of fertilizing her, is liable to be fallen upon and sucked dry by the object of his attentions. The sperm is removed by the male from the genital aperture into a special receptacle on the terminal segment of the 2nd prosomatic appendage. Thus held out at some distance from the body, it is cautiously advanced by the male spider to the genital aperture of the female.Fig.63.—Ventral view of a male mygalomorphous spider.I to VI, The six pairs of prosomatic appendages.a, Copulatory apparatus of the second appendage.b, Process of the fifth joint of the third appendage.M, Mouth.pro, Prosternite of the prosoma.mes, Mesosternite of the prosoma: observe the contact of the coxae of the sixth pair of limbs behind it; compareLiphistius(fig. 61) where this does not occur.stg, Lung aperture.gn, Genital aperture.a, Anus with a pair of backwardly migrated spinning appendages on each side of it; compare the position of these appendages inLiphistius(fig. 61).(From Lankester, “Limulus an Arachnid.”)Fig.64.—Liphistius desultor. Under side of the uplifted genital or first opisthosomatic somite of the female;g, genital aperture;p, pitted plate, probably a gland for the secretion of adhesive material for the eggs;l, the edges of the lamellae of the lung-books of the first pair.(Original drawing by Pocock.)For an account of the courtship and dancing of spiders, of their webs and floating lines, the reader is referred to the works of M‛Cook (30) and the Peckhams (31), whilst an excellent account of the nests of trap-door spiders is given by Moggridge (32). References to systematic works will also be found at the end of this article (33).Order 4. Palpigradi = Microthelyphonidae(see fig. 65).—Prosoma covered above by three plates, a larger representing the dorsal elements of the first four somites, and two smaller representing the dorsal elements of the 5th and 6th.Its ventral surface provided with one prosternal, two mesosternal and one metasternal plate. Appendages of 1st pair consisting of three segments, completely chelate, without poison gland; of 2nd pair slender, leg-like, tipped with three claws, the basal segment without sterno-coxal process taking no share in mastication, and widely separated from its fellow of the opposite side; 3rd, 4th, 5th and 6th appendages similar in form to the 2nd and to each other.Proboscis free, not supported from below by either the prosternum or the basal segments of the appendages of the 2nd pair.Fig.65.—Koenenia mirabilis, Grassi, one of the Palpigradi.A, Ventral view of prosoma and anterior region of opisthosoma with the appendages cut off near the base;aandb, prosternites;c, mesosternite; andd, metasternite of the prosoma;f, ventral surface of the prae-genital somite;g, sternite of the genital somite (first opisthosomatic somite).B, Dorsal view. I to VI, prosomatic appendages; 1opisth, genital somite (first opisthosomatic somite).C, Lateral view, I to VI, prosomatic appendages;a, b, c, the three tergal plates of the prosoma;prae-gen, the prae-genital somite; 1 to 10, the ten somites of the opisthosoma.D, Chelicera.(Original drawing by Pocock and Pickard-Cambridge, after Hansen and Sörensen.)Opisthosoma consisting of only ten somites, which have no tergal and sternal elements, the prae-genital somite contracted to form a “waist,” as in the Pedipalpi; the last three narrowed to form a caudal support for the many-jointed flagelliform telson, as in the Urotricha. Respiratory organs atrophied.Family—Koeneniidae (Koenenia).Remarks.—An extremely remarkable minute form originally described by Grassi (34) from Sicily, and since further described by Hansen (35). Recently the genus has been found in Texas, U.S.A. Only one genus of the order is known.Order 5. Solifugae = Mycetophorae(see figs. 66 to 69).—Dorsal area of prosoma covered with three distinct plates, two smaller representing the terga of the 5th and 6th somites, and a larger representing those of the anterior four somites, although the reduced terga of the 3rd and 4th are traceable behind the larger plate. The latter bears a pair of median eyes and obsolete lateral eyes on each side. Sternal elements of prosoma almost entirely absent, traces of a prosternum and metasternum alone remaining. Rostrum free, not supported by either the prosternum or the basal segments of the appendages. Appendages of 1st pair large, chelate, bisegmented, articulated to the sides of the head-shield; appendages of 2nd pair simple, pediform, with protrusible (? suctorial) organ, and no claws at the tip; their basal segments united in the middle line and furnished with sterno-coxal process. Remaining pairs of appendages with their basal segments immovably fixed to the sternal surface, similar in form, the posterior three pairs furnished with two claws supported on long stalks; the basal segments of the 6th pair bearing five pairs of tactile sensory organs or malleoli. The prae-genital somite is suppressed. Opisthosoma composed of ten somites. Respiratory organs tracheal, opening upon the ventral surface of the 2nd and 3rd, and sometimes also of the 4th somite of the opisthosoma. A supplementary pair of tracheae opening behind the basal segment of the 4th appendage of the prosoma.(? Intromittent organ of male lodged on the dorsal side of the 1st pair of prosomatic appendages.)Families—Hexisopodidae (Hexisopus). Solpugidae (Solpuga,Rhagodes). Galeodidae (Galeodes).Remarks.—These most strange-looking Arachnids occur in warmer temperate, and tropical regions of Asia, Africa and America. Their anatomy has not been studied, as yet, by means of freshly-killed material, and is imperfectly known, though the presence of the coxal glands was determined by Macleod in 1884. The proportionately enormous chelae (chelicerae) of the first pair of appendages are not provided with poison glands; their bite is not venomous.Fig.66.—Galeodes sp., one of the Solifugae. Ventral view to show legs and somites.I to VI, The six leg-bearing somites of the prosoma.opisth1, First or genital somite of the opisthosoma.ge, Site of the genital aperture.st, Thoracic tracheal aperture.l2, Anterior tracheal aperture of the opisthosoma in somite 2 of the opisthosoma.l3, Tracheal aperture in somite 3 of the opisthosoma.a, Anus.(From Lankester, “Limulus an Arachnid.”)Fig.67.—Galeodes sp., one of the Solifugae. Ventral view with the appendages cut off at the base.Fig.68.—Galeodes sp., one of the Solifugae. Dorsal view.I to VI, Prosomatic appendages.s, Prosomatic stigma or aperture of the tracheal system.1, First opisthosomatic sternite covering the genital apertureg.2, Second opisthosomatic sternite covering the second pair of tracheal aperturessp1.sp2, The third pair of tracheal apertures.10, The tenth opisthosomatic somite.an, The anal aperture.I to VI, Bases of the prosomatic appendages.o, Eyes.a, Lateral region of the cephalic plate to which the first pair of appendages are articulated.b, Cephalic plate with median eye.c, Dorsal element of somites bearing third and fourth pairs of appendages.d, Second plate of the prosoma with fifth pair of appendages.e, Third or hindermost plate of the prosoma beneath which the sixth pair of legs is articulated.1, 2, 9, 10, First, second, ninth and tenth somites of the opisthosoma.an, Anus.(Original by Pickard-Cambridge and Pocock.)(Original.)Galeodeshas been made the means of a comparison between the structure of the Arachnida and Hexapod insects by Haeckel and other writers, and it was at one time suggested that there was a genetic affinity between the two groups—throughGaleodes, or extinct forms similar to it. The segmentation of the prosoma and the form of the appendages bear a homoplastic similarity to the head, pro-, meso-, and meta-thorax of a Hexapod with mandibles, maxillary palps and three pairs of walking legs; while the opisthosoma agrees in form and number of somites with the abdomen of a Hexapod, and the tracheal stigmata present certain agreements in the two cases. Reference to literature (36).Fig.69.—Galeodes sp., one of the Solifugae.I to VI, The six prosomatic limbs cut short.o, The eyes.b,c, Demarcated areae of the cephalic or first prosomatic plate corresponding respectively to appendages I, II, III, and to appendage IV (see fig. 68).d, Second plate of the prosoma-carrying appendage V.e, Third plate of the prosoma-carrying appendage VI. The prae-genital somite is absent.1, First somite of the opisthosoma.2, Second do.S, Prosomatic tracheal aperture between legs IV and V.S′ and S″, Opisthosomatic tracheal apertures.10, Tenth opisthosomatic somite.an, Anus.(Original.)Fig.70.—Garypus litoralis, one of the Pseudoscorpiones. Ventral view.Fig.71.—Garypus litoralis, one of the Pseudoscorpiones. Dorsal view.I to VI, Prosomatic appendages.o, Sterno-coxal process of the basal segment of the second appendage.1, Sternite of the genital or first opisthosomatic somite; the prae-genital somite, though represented by a tergum, has no separate ternal plate.2 and 3, Sternites of the second and third somites of the opisthosoma, each showing a tracheal stigma.10 and 11, Sternites of the tenth and eleventh somites of the opisthosoma.an, Anus.I to VI, The prosomatic appendages.o, Eyes.prae-gen, Prae-genital somite.1, Tergite of the genital or first opisthosomatic somite.10, Tergite of the tenthsomite of the opisthosoma.11, The evanescent eleventh somite of the opisthosoma.an, Anus.(Original by Pocock and Pickard-Cambridge.)(Original.)Order 6. Pseudoscorpiones = Chelonethi,also called Chernetidia (see figs. 70, 71, 72).—Prosoma covered by a single dorsal shield, at most furnished with one or two diplostichous lateral eyes; sternal elements obliterated or almost obliterated. Appendages of the 1st pair bisegmented completely chelate, furnished with peculiar organs, theserrulaand thelamina. Appendages of 2nd pair very large and completely chelate, their basal segments meeting in the middle line, as in the Uropygi, and provided in front with membranous lip-like processes underlying the proboscis. Appendages of the 3rd, 4th, 5th and 6th pairs similar in form and function, tipped with two claws, their basal segments in contact in the median ventral line. The prae-genital somite wide, not constricted, with large tergal plate, but with its sternal plate small or inconspicuous. Opisthosomacomposed, at least in many cases, of eleven somites, the 11th somite very small, often hidden within the both. Respiratory organs in the form of tracheal tubes opening by a pair of stigmata in the 2nd and 3rd somites of the opisthosoma. Intromittent organ of male beneath sternum of the 1st somite of the opisthosoma.Sub-ordera. Panctenodactyli.—Dorsal plate of prosoma (carapace) narrowed in front; the appendages of the 1st pair small, much narrower, taken together, than the posterior border of the carapace. Serrula on movable digit of appendages of 1st pair fixed throughout its length, and broader at its proximal than at its distal end; the immovable digit with an external process.Family—Cheliferidae (Chelifer(figs. 70, 71, 72),Chiridium).”   Garypidae (Garypus).Fig.72.—Garypus litoralis, one of the Pseudoscorpiones. Lateral view.I to VI, of the six prosomatic appendages.o, Eyes.prae-gen, Tergite of the prae-genital somite.1, Genital or first opisthosomatic somite.2, 3, 10, The second, third and tenth somites of the opisthosoma.11, The minute eleventh somite;an, the anus.(Original.)Sub-orderb. Hemictenodactyli.—Dorsal plate of prosoma scarcely narrowed in front; the appendages of the 1st pair large, not much narrower, taken together, than the posterior border of the carapace. The serrula or the movable digit free at its distal end, narrowed at the base; no external lamina on the immovable digit.Family—Obisiidae (Obisium, Pseudobisium).”   Chthoniidae (Chthonius, Tridenchthonius).Remarks.—The book-scorpions—so called because they were, in old times, found not unfrequently in libraries—are found in rotten wood and under stones. The similarity of the form of their appendages to those of the scorpions suggests that they are a degenerate group derived from the latter, but the large size of the prae-genital somite in them would indicate a connexion with forms preceding the scorpions. Reference to literature (37).Fig.73.—Cryptostemma Karschii, one of the Podogona. Dorsal view of male.III to VI, The third, fourth, fifth and sixth appendages of the prosoma.a, Movable (hinged) sclerite (so-called hood) overhanging the first pair of appendages.b, Fused terga of the prosoma followed by the opisthosoma of four visible somites.an, Orifice within which the caudal segments are withdrawn.E, Extremity of the fifth appendage of the male modified to subserve copulation.(Original drawing by Pocock and Pickard-Cambridge.)Order 7. Podogona = Ricinulei(see figs. 73 to 76).—Dorsal area of prosoma furnished with two shields, a larger behind representing, probably, the tergal elements of the somites, and a smaller in front, which is freely articulated to the former and folds over the appendages of the 1st pair. Ventral area without distinct sternal plates. Appendages of 1st pair, bisegmented, completely chelate. Appendages of 2nd pair, with their basal segments uniting in the middle line below the mouth, weakly chelate at apex. Appendages of 3rd, 4th, 5th and 6th pairs similar in form; their basal segments in contact in the middle line and immovably welded, except those of the 3rd pair, which have been pushed aside so that the bases of the 2nd and 4th pairs are in contact with each other. A movable membranous joint between the prosoma and the opisthosoma, the generative aperture opening upon the ventral side of the membrane. Prae-genital somite suppressed; the opisthosma consisting of nine segments, whereof the first and second are almost suppressed and concealed within the joint between the prosoma and the opisthosoma; the following four large and manifest, and the remaining three minute and forming a slender generally-retracted tail like that ofThelyphonus. Respiratory organs tracheal, opening by a pair of spiracles in the prosoma above the base of the fifth appendage on each side. Intromittent organ of male placed at the distal end of the appendage of the 5th pair.Family—Cryptostemmidae (Cryptostemma, Poliochera), Carboniferous.Fig.74.—Cryptostemma Karschii, anterior aspect of the prosoma with the “hood” removed. I to IV, first to fourth appendages of the prosoma;a, basal segment of the second pair of appendages meeting its fellow in the middle line (see fig. 75).(Original drawing by Pocock and Pickard-Cambridge.)Remarks on the Podogona.—The name given to this small but remarkable group has reference to the position of the male intromittent organ (fig. 73,E). They are small degenerate animals with a relatively firm integument. Not more than four species and twice that number of specimens are known. They have been found in West Africa and South America. A fact of special interest in regard to them is that the genus Poliochera, from the Coal Measures, appears to be a member of the same group. The name Cryptostemma, given to the first-known genus of the order, described by Guérin-Méneville, refers to the supposed concealment of the eyes by the movable cephalic sclerite. Reference to literature (38).Fig.75.—Cryptostemma Karschii, one of the Podogona. Ventral view.I to VI, The six pairs of appendages of the prosoma, the last three cut short.1, 2, 3, 4, The four somites of the opisthosoma.a. Visible hood overhanging the first pair of appendages.b, Position of the genital orifice.c, Part of 3rd appendage.d, Fourth segment of 2nd appendage. Observe that the basal segment of appendage III doesnotmeet its fellow in the middle line.(Original drawing by Pocock and Pickard-Cambridge.)Fig.76.—Cryptostemma Karschii. Extremity of the fifth pair of appendages of the female for comparison with that of the male E in fig. 73.Order 8. Opilione(see fig. 77).—Dorsal area of prosoma covered by a single shield usually bearing a pair of eyes. Sternal elements much reduced. Appendages of 1st pair large, three segmented and completely chelate; of 2nd pair either simple and pediform, or prehensile and subchelate; of remaining four pairs, similar in form, ambulatory in function; the basal segment of the 2nd, 3rd and sometimes of the 4th pairs of appendages furnished with sterno-coxal (maxillary) lobe. Opisthosoma confluent throughout its breadth with the prosoma, with the dorsal plate of which its anterior tergal plates are more or less fused; at most ten opisthosomatic somites traceable; the generative aperture thrust far forwards between the basal segments of the 6th appendages. Prae-genital somite suppressed. Respiratory organs tracheal, opening by a pair of stigmata situated immediately behind the basal segments of the 6th pair of appendages on what is probably the sternum of the 2nd opisthosomatic somite and also in some cases upon the 5th segment of the legs.Intromittent organ of male lying within the genital orifice.Sub-ordera. Laniatores.—Orifice of foetid glands opening above the coxa of the 4th appendage, not raised upon a tubercle. Orifice of coxal gland situated just behind that of the foetid gland. Sternal plate of prosoma long and narrow, with a distinct prosternal element underlying the mouth. Coxae of 4th, 5th and 6th appendages immovable. Appendages of 2nd pair, strong, usually prehensile and spiny. Genital orifice covered by an operculum.Families—Gonoleptidae (Gonoleptes, Goniasoma).Biantidae (Biantes).Oncopodidae (Oncopus, Pelitnus).Trioenonychidae (Trioenonyx, Acumontia).Sub-orderb. Palpatores.—Orifice of foetid glands opening above the coxa of the 3rd appendage, not raised upon a tubercle. Orifice of coxal gland situated between the coxae of the 5th and 6th appendages. Sternal plate of prosoma usually short and wide, rarely longer than broad; with a larger or smaller prosternal element underlying the mouth. Coxae of 3rd, 4th, 5th and 6th appendages movableor immovable. Appendages of 2nd pair weak, pediform not prehensile. Genital orifice covered by an operculum.Families—Phalangiidae (Phalangium, Gagrella).Ischyropsalidae (Ischyropsalis, Taracus).Nemastomidae (Nemastoma).Trogulidae (Trogulus, Anelasmocephalus).Sub-orderc. Cyphophthalmi(Anepignathi).—Orifice of foetid glands opening on a tubercle situated near the lateral border of the carapace above the base of the 5th appendage. Orifice of coxal gland probably situated at base of coxa of 5th appendage; sternal plate of prosema minute or absent; no prosternal element underlying the mouth. Coxae of 5th and 6th, and usually also of 4th appendages immovable. Appendages of 2nd pair weak, pediform, not prehensile. Genital orifice not covered by an operculum.Families—Sironidae (Siro, Pettalus).Stylocellidae (Stylocellus).Remarks on the Opiliones.—These include the harvest-men, sometimes called also daddy-long-legs, with round undivided bodies and very long, easily-detached legs. The intromittent organs of the male are remarkable for their complexity and elaboration. The confluence of the regions of the body and the dislocation of apertures from their typical position are results of degeneration. The Opiliones seem to lead on from the Spiders to the Mites. Reference to literature (39).Fig.77.—Stylocellus sumatranus, one of the Opiliones; after Thorell. Enlarged.A, Dorsal view; I to VI, the six prosomatic appendages.B, Ventral view of the prosoma and of the first somite of the opisthosoma, with the appendages I to VI cut off at the base;a, tracheal stigma;mx, maxillary processes of the coxae of the 3rd pair of appendages;g, genital aperture.C, Ventral surface of the prosoma and opisthosoma;a, tracheal stigma;b, last somite.D, Lateral view of the 1st and 2nd pair of appendages.E, Lateral view of the whole body and two 1st appendages, showing the fusion of the dorsal elements of the prosoma into a single plate, and of those of the opisthosoma into an imperfectly segmented plate continuous with that of the prosoma.Apparently related to the Opiliones are two extinct groups, the Anthracomarti and Phalangiotarbi, which are not known to have survived the Carboniferous period. In the Anthracomarti the opisthosoma was movably articulated to the prosoma, and consisted of from eight to ten segments furnished with movable lateral plates, the anal segment being overlapped dorsally by a laminate expansion of the preceding segment. The carapace of the prosoma was unsegmented and often bore a pair of eyes. The appendages of the 2nd pair were slender and pediform; those of the 3rd, 4th, 5th and 6th pairs were similar in form and ambulatory in function with their basal segments arranged round a sternal area as in the order Araneae. The best-known genera wereAnthracomartusandEophognus.In the Phalangiotarbi the appendages resembled those of the Anthracomarti, except that the basal segments of the last four pairs were usually approximated in the middle line leaving a long and narrow sternal area between; and the carapace of the prosoma was unsegmented. The prosoma and opisthosoma were broadly confluent and probably immovably welded together. The opisthosoma consisted of eight or nine segments, whereof the anterior five or six were very short in the dorsal region, and the posterior three exceptionally large with the anal orifice terminal.Several genera have been established, the best-characterized beingGeraphognusandArchitarbus.Order 9. Rhynchostomi = Acari(see fig. 78).—Degenerate Arachnids resembling the Opiliones in many structural points, but chiefly distinguishable from them by the following features:—The basal segments of the appendages of the 2nd pair are united in the middle line behind the mouth, those of the 3rd, 4th, 5th and 6th pairs are widely separated and not provided with sterno-coxal (maxillary) lobes, and take no share in mastication; the respiratory stigmata, when present, belong to the prosoma, and the primitive segmentation of the opisthosoma has entirely or almost entirely disappeared.Sub-ordera.Notostigmata.—Opisthosoma consisting of ten segments defined by integumental grooves, each of the anterior four of these furnished with a single pair of dorsally-placed spiracles or tracheal stigmata.Family—Opilioacaridae (Opilioacarus).Sub-orderb.Cryptostigmata.—Integument hard, strengthened by a continuously chitinized dorsal and ventral sclerite. Tracheae typically opening by stigmata situated in the articular sockets (acetabula) of the 3rd, 4th, 5th and 6th pairs of appendages.Family—Oribatidae (Oribata, Nothrus, Hoplophora).Sub-orderc.Metastigmata.—Integument mostly like that of the Cryptostigmata. Tracheae opening by a pair of stigmata situated above and behind the base of the 4th or 5th or 6th pair of appendages.Families—Gamasidae (Gamasus, Pteroptus).Argasidae (Argas, Ornithodoros).Ixodidae (Ixodes, Rhipicephalus).Sub-orderd.Prostigmata.—Integument soft, strengthened by special sclerites, those on the ventral surface of the prosoma apparently representing the basal segments of the legs embedded in the skin. Tracheae, except in the aquatic species in which they are atrophied, opening by a pair of stigmata situated close to or above the base of the appendages of the 1st pair (mandibles).Families—Trombidiidae (Trombidium, Tetranychus).Hydrachnidae (Hydrachna, Atax).Halacaridae (Halacarus, Leptognathus).Bdellidae (Bdella, Eupodes).Fig.78.—Holothyrus nitidissimus, one of the Acari; after Thorell.A, Lateral view with appendages III to VI removed; 1, plate covering the whole dorsal area, representing the fused tergal sclerites of the prosoma and opisthosoma; 2, similarly-formed ventral plate; 3, tracheal stigma.B, Dorsal view of the same animal; II to VI, 2nd to 6th pairs of appendages. The 1st pair of appendages both in this and in C are retracted.C, Ventral view of the same; II to VI as in B;a, genital orifice;b, anus;c, united basal segments of the second pair of appendages;d, basal segment of the 6th prosomatic appendage of the right side. The rest of the appendage, as also of app. Ill, IV and V, has been cut away.Sub-ordere.Astigmata.—Degenerate, mostly parasitic forms approaching the Prostigmata in the development of integumental sclerites and the softness of the skin, but with the respiratory system absent.Families—Tyroglyphidae (Tyroglyphus, Rhizoglyphus).Sarcoptidae (Sarcoptes, Analges).Sub-orderf.Vermiformia.—Degenerate atracheate parasitic forms with the body produced posteriorly into an annulated caudal prolongation, and the 3rd, 4th, 5th and 6th pairs of appendages short and only three-jointed.Family—Demodicidae (Demodex).Sub-orderg.Tetrapoda.—Degenerate atracheate gall-mites in which the body is produced posteriorly and annulated, as inDemodex, but in which the appendages of the 3rd and 4th pairs are long and normally segmented and those of the 5th and 6th pairs entirely absent.Family—Eriophyidae (Eriophyes, Phyllocoptes).Remarks on the Rhynchostomi.—The Acari include a number of forms which are of importance and special interest on account of their parasitic habits. The ticks (Ixodes) are not only injurious as blood-suckers, but are now credited with carrying the germs of Texas cattle-fever, just as mosquitoes carry those of malaria. The itch-insect (Sarcoptes scabiei) is a well-known human parasite, so minute that it was not discovered until the end of the 18th century, and “the itch” was treated medicinally as a rash. The female burrows in the epidermis much as the female trap-door spider burrows in turf in order to make a nest in which to rear her young. The male does not burrow, but wanders freely on the surface of the skin.Demodex folliculorumis also a common parasite of the sebaceousglands of the skin of the face in man, and is frequent in the skin of the dog. Many Acari are parasitic on marine and freshwater molluscs, and others are found on the feathers of birds and the hair of mammals. Others have a special faculty of consuming dry, powdery vegetable and animal refuse, and are liable to multiply in manufactured products of this nature, such as mouldy cheese. A species of Acarus is recorded as infesting a store of powdered strychnine and feeding on that drug, so poisonous to larger organisms. Reference to literature (40).Authoritiescited by numbers in the text.—1. Strauss-Dürckheim (as reported by MM. Riester and Sanson in an appendix to the sixth volume of the French translation of Meckel’sAnatomy, 1829);2. Lankester, “Limulus an Arachnid,”Quart. Journ. Micr. Sci.vol. xxi. N.S., 1881;3.Idem, “On the Skeletotrophic Tissues of Limulus, Scorpio and Mygale,”Quart. Journ. Micr. Sci.vol. xxiv. N.S., 1884;4.Idem. Trans. Zool. Soc.vol. xi., 1883;5. Lankester and A.G. Bourne, “Eyes of Limulus and Scorpio,”Quart. Journ. Micr. Sci.vol. xxiii. N.S., Jan. 1883;6. Milne-Edwards, A., “Recherches sur l’anatomie des Limules,”Ann. Sci. Nat.5th Series,Zoologie, vol. xvii., 1873;7. Owen, Richard, “Anatomy of the King-Crab,”Trans. Linn. Soc. Lond., vol. xxviii., 1872;8. Kishinouye, “Development ofLimulus longispina,”Journal of the Science College of Japan, vol. v., 1892;9. Brauer, “Development of Scorpion,”Zeitschrift für wiss. Zoologie, vol. lix., 1895;10. Hansen, H.J., “Organs and Characters in Different Orders of Arachnida,”Entomol. Meddel.vol. iv. pp. 137-149;11. Watase, “On the Morphology of the Compound Eyes of Arthropods,”Studies from the Biolog. Lab. Johns Hopkins University, vol. iv. pp 287-334;12. Newport, George, “Nervous and Circulatory Systems in Myriapoda and Macrourous Arachnids,”Phil. Trans. Roy. Soc., 1843;13. Lankester, “Coxal Glands of Limulus, Scorpio and Mygale,”Quart. Journ. Micr. Sci.vol. xxiv. N.S., 1884;13A. W. Patten and A.P. Hazen, “Development of the Coxal Glands of Limulus,”Journ. of Morphology, vol. xvi., 1900; 13B. Bernard, “Coxal Glands of Scorpio,”Ann. and Mag. Nat. Hist.vol. xii., 1893, p. 55;14. Benham, “Testis of Limulus,”Trans. Linn. Soc., 1882;15. Lankester, “Mobility of the Spermatozoa of Limulus,”Quart. Journ. Micr. Sci.vol. xviii. N.S., 1878;16. Korschelt and Heider,Entwickelungsgeschichte(Jena, 1892),ibique citata;17. Laurie, M., “The Embryology of a Scorpion,”Quart. Journ. Micr. Sci.vol. xxxi. N.S., 1890, and “On Development ofScorpio fulvipes,”ibid.vol. xxxii., 1891;18. Lankester (Homoplasy and Homogeny), “On the Use of the term Homology in Modern Zoology,”Ann. and Mag. Nat. Hist., 1870;19.Idem, “Degeneration, a Chapter in Darwinism,” 1878, reprinted in theAdvancement of Science(Macmillan, 1890);20.Idem, “Limulus an Arachnid,”Q. J. Micr. Sci.vol. xxi. N.S.;21. Claus, “Degeneration of the Acari and Classification of Arthropoda,”Anzeiger d. k. k. Akad. Wissen. Wien, 1885; see alsoAnn. and Mag. Nat. Hist.(5) vol. xvii., 1886, p. 364, and vol. xix. p. 225;22. Lindstrom, G., “Researches on the Visual Organs of the Trilobites,”K. Svenska Vet. Akad. Handl.xxxiv. No. 8, pp. 1-86, Pls. i.-vi., 1901;22*. Zittel, American edition of hisPalaeontology(the Macmillan Co., New York), where ample references to the literature of Trilobitae and Eurypteridae will be found; also references to literature of fossil Scorpions and Spiders;23. Hoek, “Report on the Pycnogonida,”Challenger Expedition Reports, 1881; Meinert, “Pycnogonida of the Danish Ingolf Expedition,” vol. iii., 1899; Morgan, “Embryology and Phylogeny of the Pycnogonids,”Biol. Lab. Baltimore, vol. v., 1891;24. Bourne, A.G., “The Reputed Suicide of the Scorpion,”Proc. Roy. Soc.vol. xlii. pp. 17-22;25. Lankester, “Notes on some Habits of Scorpions,”Journ. Linn. Soc. Zool.vol. xvi. p. 455, 1882;26. Huxley, “Pharynx of Scorpion,”Quart. Journ. Micr. Sci.vol. viii. (old series), 1860, p. 250;27. Pocock, “How and Why Scorpions hiss,”Natural Science, vol. ix., 1896; cf.idem, “Stridulating Organs of Spiders,”Ann. and Mag. Nat. Hist.(6), xvi. pp. 230-233;28. Kraepelin,Das Thierreich (Scorpiones et Pedipalpi) (Berlin, 1899); Peters, “Eine neue Eintheilung der Skorpione,”Man. Akad. Wiss. Berlin, 1861; Pocock, “Classification of Scorpions,”Ann. and Mag. Nat. Hist.(6) xii., 1893; Thorell and Lindstrom, “On a Silurian Scorpion,”Kongl. Svens. Vet. Akad. Handl.xxi. No. 9, 1885;29. Cambridge, O.P., “A New Family (Tartarides) and Genus of Thelyphonidea,”Ann. and Mag. Nat. Hist.(4) x., 1872, p. 413; Cook, “Hubbardia, a New Genus of Pedipalpi,”Proc. Entom. Soc. Washington, vol. iv., 1899; Thorell, “Tartarides, &c.”Ann. Mus. Genova, vol. xxvii., 1889;30. M Cook,American Spiders and their Spinning Work(3 vols.; Philadelphia, 1889-1893);31. Peckham, “On Sexual Selection in Spiders,”Occasional Papers Nat. Hist. Soc. Wisconsin, vol. i. pp. 1-113, 1889;32. Moggridge,Harvesting Ants and Trap-Door Spiders(1873);33. Bertkau, Ph.,Arch. f. Naturgesch.vol. xlviii. pp. 316-362;Idem, same journal, 1875, p. 235, and 1878, p. 351; Cambridge, O.P., “Araneidea” inBiologia Centr. Americana, vols. i. and ii. (London, 1899); Keyserling,Spinnen Amerikas(Nuremberg, 1880-1892); Pocock, “Liphistius and the Classification of Spiders,”Ann. and Mag. Nat. Hist.(6) x., 1892; Simon,Hist. nat. des Araignées, vols. i. and ii., 1892, 1897; Wagner, “L’Industrie des Araneína,”Mem. Acad. St-Pétersbourg;Idem, “La Mue des Araignées,”Ann. Sci. Nat.vol. vi.;34. Grassi, G.B. “Intorno ad un nuovo Aracnide artrogastro (Koenenia mirabilis) &c.”Boll. Soc. Ent. Ital.vol. xviii., 1886;35. H.J. Hansen and Sörensen, “The Order Palpigradi, Thorell (Koenenia), and its Relationships with other Arachnida,”Ent. Tidskr.vol. xviii. pp. 233-240, 1898; Kraepelin,Das Thierreich(Berlin, 1901);36. Bernard. “Compar. Morphol. of the Galeodidae,”Trans. Linn. Soc. Zool.vol. vi., 1896,ibique citata; Dufour, “Galeodes,”Mém. prés. Acad. Sci. Paris, vol. xvii., 1862; Kraepelin,Das Thierreich(Berlin, 1901); Pocock, “Taxonomy of Solifugae,”Ann. and Mag. Nat. Hist.vol. xx.;37. Balzan, “Voyage au Vénézuela (Pseudoscorpiones),”Ann. Soc. Entom. France, 1891, pp. 497-522;38. Guérin-Méneville,Rev. Zool., 1838, p. II; Karsch, “Ueber Cryptostemma Guer.”Berliner entom. Zeitschrift, xxxviii. pp. 25-32, 1892; Thorell, “On an apparently new Arachnid belonging to the familyCryptostemmidae,”Westv. Bihang Svenska Vet. Akad. Handligar, vol. xvii. No. 9, 1892;39. Hansen and Sorensen,On Two Orders of Arachnida(Cambridge, 1904); Sörensen, “Opiliones laniatores,”Nat. Tidskr.(3) vol. xiv., 1884; Thorell, “Opilioni,”Ann. Mus. Genova, vol. viii., 1876;40. Berlese, “Acari, &c., in Italia reperta” (Padova, 1892); Canestrini,Acarofauna Italiana(Padova, 1885); Canestrini and Kramer, “Demodicidae and Sarcoptidae” inDas Thierreich(Berlin, 1899); Michael, “British Oribatidae,”Ray Soc.;Idem, “Oribatidae” inDas Thierreich(Berlin, 1898);Idem, “Progress and Present State of Knowledge of Acari,”Journ. Roy. Micr. Soc., 1894; Nalepa, “Phytoptidae,”Das Thierreich(Berlin, 1898); Trouessart, “Classification des Acariens,”Rev. Sci. Nat. de l’ouest.p. 289, 1892; Wagner,Embryonal Entwick, von Ixodes(St Petersburg, 1803);41. Bertkau, Ph., “Coxaldrusen der Arachniden,”Sitzb. Niederl. Gesellsch., 1885;42. Patten, W., “Brain and Sense Organs of Limulus,”Quart. Journ. Mic. Sci.vol. xxxv., 1894; see also his “Origin of Vertebrates from Arachnids,”ibid.vol. xxxi.Authorities not cited by numbers in the text:—Lung-books:—Berteaux, “Le Poumon des Arachnides,”La Cellule, vol. v. 1891; Jawarowski, “Die Entwick. d. sogen. Lunge bei der Arachniden,”Zeitsch. wiss. Zool.vol. lviii., 1894; Macleod, “Recherches sur la structure et la signification de l’appareil respiratoire des Arachnides,”Arch. d. Biologie.vol. v., 1884; Schneider, A., “Mélanges arachnologiques,” inTablettes zoologiques, vol. ii. p. 135, 1892; Simmons, “Development of Lung in Spiders,”Amer. Journ. Science, vol. xlviii., 1894.Coxal Glands:—Bertkau, “Ueber die Coxaldrusen der Arachniden,”Sitzb. d. Niederl. Gesellsch., 1885; Loman, “Altes und neues über das Nephridium (die Coxaldrüse) der Arachniden,”Bÿd. tot de Dierkunde, vol. xiv., 1887; Macleod, “Glande coxale chez les Galéodes,”Bull. Acad. Belg.(3) vol. viii., 1884; Pelseneer, “On the Coxal Glands of Mygale,”Proc. Zool. Soc., 1885; Tower, “The External Opening of the brick-red Glands of Limulus,”Zool. Anzeiger, vol. xviii. p. 471, 1895.Ento-sternite:—Schimkewitsch, “Bau und Entwick. des Endosternites der Arachniden,”Zool. Jahrb., Anal. Abtheil., vol. viii., 1894.Embryology:—Balfour, “Development of the Araneina,”Q. J. Micr. Sci.vol. xx., 1880; Kingsley, “The Embryology of Limulus,”Journ. Morphology, vols. vii. and viii.; Kishinouye, “Development of Araneina,”Journ. Coll. Sci. Univ. of Japan, vol. iv., 1890; Locy, “Development of Agelena,”Bull. Mus. Harvard, vol. xii., 1885; Metchnikoff, “Embryologie d. Scorpion,”Zeit. wiss. Zool.vol. xxi., 1871;Idem, “Embryol. Chelifer,”Zeit. wiss. Zool.vol. xxi., 1871; Schimkewitsch, “Développement des Araignées,”Archives d. Biologie, vol. vi. 1887.Sense organs:—Bertkau, “Sinnesorgane der Spinnen,”Arch. f. mikros. Anat.vol. xxvii. p. 589, 1886; Graber, “Unicorneale Tracheaten Auge,”Arch. f. mikr. Anat.vol. xvii., 1879; Grenacher,Gehörorgane der Arthropoden(Göttingen, 1879); Kishinouye, “Lateral Eyes of Spiders,”Zool. Anz.vol. xiv. p. 381, 1891; Purcell, “Phalangiden Augen,”Zool. Anzeiger, vol. xv. p. 461.General works on Arachnida:—Blanchard, “Les Arachnides” inL’Organisation du regne animal; Gaubert, “Recherches sur les Arachnides,”Ann. Sci. Nat.(7) vol. xiii., 1892; Koch, C.,Die Arachniden(16 vols., Nuremberg, 1831-1848); Koch, Keyserling and Sörensen,Die Arachniden Australiens(Nuremberg, 1871-1890); Pocock,Arachnida of British India(London, 1900);Idem, “On African Arachnida,” inProc. Zool. Soc.andAnn. and Mag. Nat. Hist., 1897-1900; Simon,Les Arachnides de la France(7 vols., Paris, 1874-1881); Thorell, “Arachnida from the Oriental Region,”Ann. Mus. Genova, 1877-1899.

Family—Phrynichidae (Phrynichus,Damon).”   Admetidae (Admetus,Heterophrynus).”   Charontidae (Charon,Sarax).(Family ?)—*Graeophonus.

Family—Phrynichidae (Phrynichus,Damon).

”   Admetidae (Admetus,Heterophrynus).

”   Charontidae (Charon,Sarax).

(Family ?)—*Graeophonus.

Remarks.—The Pedipalpi are confined to the tropics and warmer temperate regions of both hemispheres. Fossil forms occur in the Carboniferous. The small forms known asSchizomusandHubbardiaare of special interest from a morphological point of view. The Pedipalpi have no poison glands. (Reference to literature (29).)

Order 3. Araneae(figs. 60 to 64.).—Prosoma covered with a single shield and typically furnished with median and lateral eyes of diplostichous structure, as in the Amblypygi. The sternal surface wide, continuously chitinized, but with prosternal and metasternal elements generally distinguishable at the anterior and posterior ends respectively of the large mesosternurm. Prosternum underlying the proboscis. Appendages of 1st pair have two segments, as in Pedipalpi, but are furnished with poison gland, and are retroverts. Appendages of 2nd pair not underlying the mouth, but freely movable and, except in primitive forms, furnished with a maxillary lobe; the rest of the limb like the legs, tipped with a single claw and quite unmodified (except in ♂). Remaining pairs of appendages similar in form and function, each tipped with two or three claws. Opisthosoma when segmented showing the same number of somites as in the Pedipalpi; usually unsegmented, the prae-genital somite constricted to form the waist; the appendages of its 3rd and 4th somites retained as spinning mammillae. Respiratory organs (see fig. 63,stg), as in the Amblypygi, or with the posterior pair, rarely the anterior pair as well, replaced by tracheal tubes. Intromittent organ of male in the apical segment of the 2nd prosomatic appendage.

Sub-ordera. Mesothelae (see figs. 60 to 62).—Opisthosoma distinctly segmented, furnished with 11 tergal plates, as in the Amblypygi; the ventral surface of the 1st and 2nd somites with large sternal plates, covering the genital aperture and the two pairs of pulmonary sacs, the sternal plates from the 6th to the 11th somites represented by integumental ridges, weakly chitinized in the middle. The two pairs of spinning appendages retain their primitive position in the middle of the lower surface of the opisthosoma far in advance of the anus on the 3rd and 4th somites, each appendage consisting of a stout, many-jointed outer branch and a slender, unsegmented inner branch. Prosoma as in the Mygalomorphae, except that the mesosternal area is long and narrow.

Family—Liphistiidae (Liphistius, *Arthrolycosa).

Family—Liphistiidae (Liphistius, *Arthrolycosa).

Sub-orderb. Opisthothelae (see fig. 63).—Opisthosoma without trace of separate terga and sterna, the segmentation merely represented posteriorly by slight integumental folds and the sterna of the 1st and 2nd somites by the opercular plates of the pulmonary sacs. The spinning appendages migrate to the posterior end of the opisthosoma and take up a position close to the anus; the inner branches of the anterior pair either atrophy or are represented homogenetically by a plate, the cribellum, or by an undivided membranous lobe, the colulus.

I to VI, Appendages of the prosoma cut off at the base.

o, Ocular tubercle.

prae-gen, The prae-genital somite.

1 and 2, Sternites of the first and second opisthosomatic somites.

3 and 4, Appendages of the third and fourth opisthosomatic somites, which are the spinning organs, and in this genus occupy their primitive position instead of migrating to the anal region as in other spiders.

5, Tergite of the fifth opisthosomatic somite.

11, Eleventh opisthosomatic somite;an, Anus.

Tribe 1. Mygalomorphae.—The plane of the articulation of the appendages of the 1st pair to the prosoma (the retrovert) vertical, the basal segment projecting straight forwards at its proximal end, the distal segment or fang closing backwards in a direction subparallel to the long axis of the body. Two pairs of pulmonary sacs.

Families—Theraphosidae (Avicularia,Poecilotheria). Barychelidae (Barychelus,Plagiobothrus). Dipluridae (Diplura,Macrothele). Ctenizidae (Cteniza,Nemesia). Atypidae (Atypus,Calommata).

Tribe 2. Arachnomorpnae.—The plane of the articulation of the appendages of the 1st pair to the prosoma horizontal, the basal segment projecting vertically downwards, at least at its proximal end, the distal segment or fang closing inwards nearly or quite at right angles to the long axis of the body. The posterior pulmonary sacs (except inHypochilus) replaced by tracheal tubes; the anterior and posterior pairs replaced by tracheal tubes in the Caponiidae.

Principal families—Hypochilidae (Hypochilus). Dysderidae (Dysdera,Segestria). Caponiidae (Caponia,Nops). Filistatidae (Filistata). Uloboridae (Uloborus,Dinopis). Argiapidae (Nephila,Gasteracantha). Pholcidae (Pholcus,Artema). Agelenidae (Tegenuria). Lycosidae (Lycosa). Clubionidae (Clubiona,Olios,Sparassus) Gnaphosidae (Gnaphosa,Hemiclaea). Thomisidae (Thomisus). Attidae (Salticus). Urocteidae (Uroctea). Eresidae (Eresus).

Remarks on the Araneae.—The Spiders are the most numerousand diversified group of the Arachnida; about 2000 species are known. No noteworthy fossil spiders are known; the best-preserved are in amber of Oligocene age.ProtolycosaandArthrolycosaoccur in the Carboniferous. Morphologically, the spiders are remarkable for the concentration and specialization of their structure, which is accompanied with high physiological efficiency. The larger species of Bird’s Nest Spiders (Avicularia), the opisthosoma of which is as large as a bantam’s egg, undoubtedly attack young birds, and M’Cook gives an account of the capture in its web by an ordinary house spider of a small mouse. The “retrovert” or bent-back first pair of appendages is provided with a poison gland opening on the fang or terminal segment. Spiders form at least two kinds of constructions—snares for the capture of prey and nests for the preservation of the young. The latter are only formed by the female, which is a larger and more powerful animal than the male. Like the scorpions the spiders have a special tendency to cannibalism, and accordingly the male, in approaching the female for the purpose of fertilizing her, is liable to be fallen upon and sucked dry by the object of his attentions. The sperm is removed by the male from the genital aperture into a special receptacle on the terminal segment of the 2nd prosomatic appendage. Thus held out at some distance from the body, it is cautiously advanced by the male spider to the genital aperture of the female.

I to VI, The six pairs of prosomatic appendages.

a, Copulatory apparatus of the second appendage.

b, Process of the fifth joint of the third appendage.

M, Mouth.

pro, Prosternite of the prosoma.

mes, Mesosternite of the prosoma: observe the contact of the coxae of the sixth pair of limbs behind it; compareLiphistius(fig. 61) where this does not occur.

stg, Lung aperture.

gn, Genital aperture.

a, Anus with a pair of backwardly migrated spinning appendages on each side of it; compare the position of these appendages inLiphistius(fig. 61).

For an account of the courtship and dancing of spiders, of their webs and floating lines, the reader is referred to the works of M‛Cook (30) and the Peckhams (31), whilst an excellent account of the nests of trap-door spiders is given by Moggridge (32). References to systematic works will also be found at the end of this article (33).

Order 4. Palpigradi = Microthelyphonidae(see fig. 65).—Prosoma covered above by three plates, a larger representing the dorsal elements of the first four somites, and two smaller representing the dorsal elements of the 5th and 6th.

Its ventral surface provided with one prosternal, two mesosternal and one metasternal plate. Appendages of 1st pair consisting of three segments, completely chelate, without poison gland; of 2nd pair slender, leg-like, tipped with three claws, the basal segment without sterno-coxal process taking no share in mastication, and widely separated from its fellow of the opposite side; 3rd, 4th, 5th and 6th appendages similar in form to the 2nd and to each other.

Proboscis free, not supported from below by either the prosternum or the basal segments of the appendages of the 2nd pair.

A, Ventral view of prosoma and anterior region of opisthosoma with the appendages cut off near the base;aandb, prosternites;c, mesosternite; andd, metasternite of the prosoma;f, ventral surface of the prae-genital somite;g, sternite of the genital somite (first opisthosomatic somite).

B, Dorsal view. I to VI, prosomatic appendages; 1opisth, genital somite (first opisthosomatic somite).

C, Lateral view, I to VI, prosomatic appendages;a, b, c, the three tergal plates of the prosoma;prae-gen, the prae-genital somite; 1 to 10, the ten somites of the opisthosoma.

D, Chelicera.

Opisthosoma consisting of only ten somites, which have no tergal and sternal elements, the prae-genital somite contracted to form a “waist,” as in the Pedipalpi; the last three narrowed to form a caudal support for the many-jointed flagelliform telson, as in the Urotricha. Respiratory organs atrophied.

Family—Koeneniidae (Koenenia).

Family—Koeneniidae (Koenenia).

Remarks.—An extremely remarkable minute form originally described by Grassi (34) from Sicily, and since further described by Hansen (35). Recently the genus has been found in Texas, U.S.A. Only one genus of the order is known.

Order 5. Solifugae = Mycetophorae(see figs. 66 to 69).—Dorsal area of prosoma covered with three distinct plates, two smaller representing the terga of the 5th and 6th somites, and a larger representing those of the anterior four somites, although the reduced terga of the 3rd and 4th are traceable behind the larger plate. The latter bears a pair of median eyes and obsolete lateral eyes on each side. Sternal elements of prosoma almost entirely absent, traces of a prosternum and metasternum alone remaining. Rostrum free, not supported by either the prosternum or the basal segments of the appendages. Appendages of 1st pair large, chelate, bisegmented, articulated to the sides of the head-shield; appendages of 2nd pair simple, pediform, with protrusible (? suctorial) organ, and no claws at the tip; their basal segments united in the middle line and furnished with sterno-coxal process. Remaining pairs of appendages with their basal segments immovably fixed to the sternal surface, similar in form, the posterior three pairs furnished with two claws supported on long stalks; the basal segments of the 6th pair bearing five pairs of tactile sensory organs or malleoli. The prae-genital somite is suppressed. Opisthosoma composed of ten somites. Respiratory organs tracheal, opening upon the ventral surface of the 2nd and 3rd, and sometimes also of the 4th somite of the opisthosoma. A supplementary pair of tracheae opening behind the basal segment of the 4th appendage of the prosoma.

(? Intromittent organ of male lodged on the dorsal side of the 1st pair of prosomatic appendages.)

Families—Hexisopodidae (Hexisopus). Solpugidae (Solpuga,Rhagodes). Galeodidae (Galeodes).

Remarks.—These most strange-looking Arachnids occur in warmer temperate, and tropical regions of Asia, Africa and America. Their anatomy has not been studied, as yet, by means of freshly-killed material, and is imperfectly known, though the presence of the coxal glands was determined by Macleod in 1884. The proportionately enormous chelae (chelicerae) of the first pair of appendages are not provided with poison glands; their bite is not venomous.

I to VI, The six leg-bearing somites of the prosoma.

opisth1, First or genital somite of the opisthosoma.

ge, Site of the genital aperture.

st, Thoracic tracheal aperture.

l2, Anterior tracheal aperture of the opisthosoma in somite 2 of the opisthosoma.

l3, Tracheal aperture in somite 3 of the opisthosoma.

a, Anus.

I to VI, Prosomatic appendages.

s, Prosomatic stigma or aperture of the tracheal system.

1, First opisthosomatic sternite covering the genital apertureg.

2, Second opisthosomatic sternite covering the second pair of tracheal aperturessp1.

sp2, The third pair of tracheal apertures.

10, The tenth opisthosomatic somite.

an, The anal aperture.

I to VI, Bases of the prosomatic appendages.

o, Eyes.

a, Lateral region of the cephalic plate to which the first pair of appendages are articulated.

b, Cephalic plate with median eye.

c, Dorsal element of somites bearing third and fourth pairs of appendages.

d, Second plate of the prosoma with fifth pair of appendages.

e, Third or hindermost plate of the prosoma beneath which the sixth pair of legs is articulated.

1, 2, 9, 10, First, second, ninth and tenth somites of the opisthosoma.

an, Anus.

Galeodeshas been made the means of a comparison between the structure of the Arachnida and Hexapod insects by Haeckel and other writers, and it was at one time suggested that there was a genetic affinity between the two groups—throughGaleodes, or extinct forms similar to it. The segmentation of the prosoma and the form of the appendages bear a homoplastic similarity to the head, pro-, meso-, and meta-thorax of a Hexapod with mandibles, maxillary palps and three pairs of walking legs; while the opisthosoma agrees in form and number of somites with the abdomen of a Hexapod, and the tracheal stigmata present certain agreements in the two cases. Reference to literature (36).

I to VI, The six prosomatic limbs cut short.

o, The eyes.

b,c, Demarcated areae of the cephalic or first prosomatic plate corresponding respectively to appendages I, II, III, and to appendage IV (see fig. 68).

d, Second plate of the prosoma-carrying appendage V.

e, Third plate of the prosoma-carrying appendage VI. The prae-genital somite is absent.

1, First somite of the opisthosoma.

2, Second do.

S, Prosomatic tracheal aperture between legs IV and V.

S′ and S″, Opisthosomatic tracheal apertures.

10, Tenth opisthosomatic somite.

an, Anus.

I to VI, Prosomatic appendages.

o, Sterno-coxal process of the basal segment of the second appendage.

1, Sternite of the genital or first opisthosomatic somite; the prae-genital somite, though represented by a tergum, has no separate ternal plate.

2 and 3, Sternites of the second and third somites of the opisthosoma, each showing a tracheal stigma.

10 and 11, Sternites of the tenth and eleventh somites of the opisthosoma.

an, Anus.

I to VI, The prosomatic appendages.

o, Eyes.

prae-gen, Prae-genital somite.

1, Tergite of the genital or first opisthosomatic somite.

10, Tergite of the tenthsomite of the opisthosoma.

11, The evanescent eleventh somite of the opisthosoma.

an, Anus.

Order 6. Pseudoscorpiones = Chelonethi,also called Chernetidia (see figs. 70, 71, 72).—Prosoma covered by a single dorsal shield, at most furnished with one or two diplostichous lateral eyes; sternal elements obliterated or almost obliterated. Appendages of the 1st pair bisegmented completely chelate, furnished with peculiar organs, theserrulaand thelamina. Appendages of 2nd pair very large and completely chelate, their basal segments meeting in the middle line, as in the Uropygi, and provided in front with membranous lip-like processes underlying the proboscis. Appendages of the 3rd, 4th, 5th and 6th pairs similar in form and function, tipped with two claws, their basal segments in contact in the median ventral line. The prae-genital somite wide, not constricted, with large tergal plate, but with its sternal plate small or inconspicuous. Opisthosomacomposed, at least in many cases, of eleven somites, the 11th somite very small, often hidden within the both. Respiratory organs in the form of tracheal tubes opening by a pair of stigmata in the 2nd and 3rd somites of the opisthosoma. Intromittent organ of male beneath sternum of the 1st somite of the opisthosoma.

Sub-ordera. Panctenodactyli.—Dorsal plate of prosoma (carapace) narrowed in front; the appendages of the 1st pair small, much narrower, taken together, than the posterior border of the carapace. Serrula on movable digit of appendages of 1st pair fixed throughout its length, and broader at its proximal than at its distal end; the immovable digit with an external process.

Family—Cheliferidae (Chelifer(figs. 70, 71, 72),Chiridium).”   Garypidae (Garypus).

Family—Cheliferidae (Chelifer(figs. 70, 71, 72),Chiridium).

”   Garypidae (Garypus).

I to VI, of the six prosomatic appendages.

o, Eyes.

prae-gen, Tergite of the prae-genital somite.

1, Genital or first opisthosomatic somite.

2, 3, 10, The second, third and tenth somites of the opisthosoma.

11, The minute eleventh somite;

an, the anus.

Sub-orderb. Hemictenodactyli.—Dorsal plate of prosoma scarcely narrowed in front; the appendages of the 1st pair large, not much narrower, taken together, than the posterior border of the carapace. The serrula or the movable digit free at its distal end, narrowed at the base; no external lamina on the immovable digit.

Family—Obisiidae (Obisium, Pseudobisium).”   Chthoniidae (Chthonius, Tridenchthonius).

Family—Obisiidae (Obisium, Pseudobisium).

”   Chthoniidae (Chthonius, Tridenchthonius).

Remarks.—The book-scorpions—so called because they were, in old times, found not unfrequently in libraries—are found in rotten wood and under stones. The similarity of the form of their appendages to those of the scorpions suggests that they are a degenerate group derived from the latter, but the large size of the prae-genital somite in them would indicate a connexion with forms preceding the scorpions. Reference to literature (37).

III to VI, The third, fourth, fifth and sixth appendages of the prosoma.

a, Movable (hinged) sclerite (so-called hood) overhanging the first pair of appendages.

b, Fused terga of the prosoma followed by the opisthosoma of four visible somites.

an, Orifice within which the caudal segments are withdrawn.

E, Extremity of the fifth appendage of the male modified to subserve copulation.

Order 7. Podogona = Ricinulei(see figs. 73 to 76).—Dorsal area of prosoma furnished with two shields, a larger behind representing, probably, the tergal elements of the somites, and a smaller in front, which is freely articulated to the former and folds over the appendages of the 1st pair. Ventral area without distinct sternal plates. Appendages of 1st pair, bisegmented, completely chelate. Appendages of 2nd pair, with their basal segments uniting in the middle line below the mouth, weakly chelate at apex. Appendages of 3rd, 4th, 5th and 6th pairs similar in form; their basal segments in contact in the middle line and immovably welded, except those of the 3rd pair, which have been pushed aside so that the bases of the 2nd and 4th pairs are in contact with each other. A movable membranous joint between the prosoma and the opisthosoma, the generative aperture opening upon the ventral side of the membrane. Prae-genital somite suppressed; the opisthosma consisting of nine segments, whereof the first and second are almost suppressed and concealed within the joint between the prosoma and the opisthosoma; the following four large and manifest, and the remaining three minute and forming a slender generally-retracted tail like that ofThelyphonus. Respiratory organs tracheal, opening by a pair of spiracles in the prosoma above the base of the fifth appendage on each side. Intromittent organ of male placed at the distal end of the appendage of the 5th pair.

Family—Cryptostemmidae (Cryptostemma, Poliochera), Carboniferous.

Family—Cryptostemmidae (Cryptostemma, Poliochera), Carboniferous.

Remarks on the Podogona.—The name given to this small but remarkable group has reference to the position of the male intromittent organ (fig. 73,E). They are small degenerate animals with a relatively firm integument. Not more than four species and twice that number of specimens are known. They have been found in West Africa and South America. A fact of special interest in regard to them is that the genus Poliochera, from the Coal Measures, appears to be a member of the same group. The name Cryptostemma, given to the first-known genus of the order, described by Guérin-Méneville, refers to the supposed concealment of the eyes by the movable cephalic sclerite. Reference to literature (38).

I to VI, The six pairs of appendages of the prosoma, the last three cut short.

1, 2, 3, 4, The four somites of the opisthosoma.

a. Visible hood overhanging the first pair of appendages.

b, Position of the genital orifice.

c, Part of 3rd appendage.

d, Fourth segment of 2nd appendage. Observe that the basal segment of appendage III doesnotmeet its fellow in the middle line.

Order 8. Opilione(see fig. 77).—Dorsal area of prosoma covered by a single shield usually bearing a pair of eyes. Sternal elements much reduced. Appendages of 1st pair large, three segmented and completely chelate; of 2nd pair either simple and pediform, or prehensile and subchelate; of remaining four pairs, similar in form, ambulatory in function; the basal segment of the 2nd, 3rd and sometimes of the 4th pairs of appendages furnished with sterno-coxal (maxillary) lobe. Opisthosoma confluent throughout its breadth with the prosoma, with the dorsal plate of which its anterior tergal plates are more or less fused; at most ten opisthosomatic somites traceable; the generative aperture thrust far forwards between the basal segments of the 6th appendages. Prae-genital somite suppressed. Respiratory organs tracheal, opening by a pair of stigmata situated immediately behind the basal segments of the 6th pair of appendages on what is probably the sternum of the 2nd opisthosomatic somite and also in some cases upon the 5th segment of the legs.

Intromittent organ of male lying within the genital orifice.

Sub-ordera. Laniatores.—Orifice of foetid glands opening above the coxa of the 4th appendage, not raised upon a tubercle. Orifice of coxal gland situated just behind that of the foetid gland. Sternal plate of prosoma long and narrow, with a distinct prosternal element underlying the mouth. Coxae of 4th, 5th and 6th appendages immovable. Appendages of 2nd pair, strong, usually prehensile and spiny. Genital orifice covered by an operculum.

Families—Gonoleptidae (Gonoleptes, Goniasoma).Biantidae (Biantes).Oncopodidae (Oncopus, Pelitnus).Trioenonychidae (Trioenonyx, Acumontia).

Families—Gonoleptidae (Gonoleptes, Goniasoma).

Biantidae (Biantes).

Oncopodidae (Oncopus, Pelitnus).

Trioenonychidae (Trioenonyx, Acumontia).

Sub-orderb. Palpatores.—Orifice of foetid glands opening above the coxa of the 3rd appendage, not raised upon a tubercle. Orifice of coxal gland situated between the coxae of the 5th and 6th appendages. Sternal plate of prosoma usually short and wide, rarely longer than broad; with a larger or smaller prosternal element underlying the mouth. Coxae of 3rd, 4th, 5th and 6th appendages movableor immovable. Appendages of 2nd pair weak, pediform not prehensile. Genital orifice covered by an operculum.

Families—Phalangiidae (Phalangium, Gagrella).Ischyropsalidae (Ischyropsalis, Taracus).Nemastomidae (Nemastoma).Trogulidae (Trogulus, Anelasmocephalus).

Families—Phalangiidae (Phalangium, Gagrella).

Ischyropsalidae (Ischyropsalis, Taracus).

Nemastomidae (Nemastoma).

Trogulidae (Trogulus, Anelasmocephalus).

Sub-orderc. Cyphophthalmi(Anepignathi).—Orifice of foetid glands opening on a tubercle situated near the lateral border of the carapace above the base of the 5th appendage. Orifice of coxal gland probably situated at base of coxa of 5th appendage; sternal plate of prosema minute or absent; no prosternal element underlying the mouth. Coxae of 5th and 6th, and usually also of 4th appendages immovable. Appendages of 2nd pair weak, pediform, not prehensile. Genital orifice not covered by an operculum.

Families—Sironidae (Siro, Pettalus).Stylocellidae (Stylocellus).

Families—Sironidae (Siro, Pettalus).

Stylocellidae (Stylocellus).

Remarks on the Opiliones.—These include the harvest-men, sometimes called also daddy-long-legs, with round undivided bodies and very long, easily-detached legs. The intromittent organs of the male are remarkable for their complexity and elaboration. The confluence of the regions of the body and the dislocation of apertures from their typical position are results of degeneration. The Opiliones seem to lead on from the Spiders to the Mites. Reference to literature (39).

A, Dorsal view; I to VI, the six prosomatic appendages.

B, Ventral view of the prosoma and of the first somite of the opisthosoma, with the appendages I to VI cut off at the base;a, tracheal stigma;mx, maxillary processes of the coxae of the 3rd pair of appendages;g, genital aperture.

C, Ventral surface of the prosoma and opisthosoma;a, tracheal stigma;b, last somite.

D, Lateral view of the 1st and 2nd pair of appendages.

E, Lateral view of the whole body and two 1st appendages, showing the fusion of the dorsal elements of the prosoma into a single plate, and of those of the opisthosoma into an imperfectly segmented plate continuous with that of the prosoma.

Apparently related to the Opiliones are two extinct groups, the Anthracomarti and Phalangiotarbi, which are not known to have survived the Carboniferous period. In the Anthracomarti the opisthosoma was movably articulated to the prosoma, and consisted of from eight to ten segments furnished with movable lateral plates, the anal segment being overlapped dorsally by a laminate expansion of the preceding segment. The carapace of the prosoma was unsegmented and often bore a pair of eyes. The appendages of the 2nd pair were slender and pediform; those of the 3rd, 4th, 5th and 6th pairs were similar in form and ambulatory in function with their basal segments arranged round a sternal area as in the order Araneae. The best-known genera wereAnthracomartusandEophognus.

In the Phalangiotarbi the appendages resembled those of the Anthracomarti, except that the basal segments of the last four pairs were usually approximated in the middle line leaving a long and narrow sternal area between; and the carapace of the prosoma was unsegmented. The prosoma and opisthosoma were broadly confluent and probably immovably welded together. The opisthosoma consisted of eight or nine segments, whereof the anterior five or six were very short in the dorsal region, and the posterior three exceptionally large with the anal orifice terminal.

Several genera have been established, the best-characterized beingGeraphognusandArchitarbus.

Order 9. Rhynchostomi = Acari(see fig. 78).—Degenerate Arachnids resembling the Opiliones in many structural points, but chiefly distinguishable from them by the following features:—The basal segments of the appendages of the 2nd pair are united in the middle line behind the mouth, those of the 3rd, 4th, 5th and 6th pairs are widely separated and not provided with sterno-coxal (maxillary) lobes, and take no share in mastication; the respiratory stigmata, when present, belong to the prosoma, and the primitive segmentation of the opisthosoma has entirely or almost entirely disappeared.

Sub-ordera.Notostigmata.—Opisthosoma consisting of ten segments defined by integumental grooves, each of the anterior four of these furnished with a single pair of dorsally-placed spiracles or tracheal stigmata.

Family—Opilioacaridae (Opilioacarus).

Family—Opilioacaridae (Opilioacarus).

Sub-orderb.Cryptostigmata.—Integument hard, strengthened by a continuously chitinized dorsal and ventral sclerite. Tracheae typically opening by stigmata situated in the articular sockets (acetabula) of the 3rd, 4th, 5th and 6th pairs of appendages.

Family—Oribatidae (Oribata, Nothrus, Hoplophora).

Family—Oribatidae (Oribata, Nothrus, Hoplophora).

Sub-orderc.Metastigmata.—Integument mostly like that of the Cryptostigmata. Tracheae opening by a pair of stigmata situated above and behind the base of the 4th or 5th or 6th pair of appendages.

Families—Gamasidae (Gamasus, Pteroptus).Argasidae (Argas, Ornithodoros).Ixodidae (Ixodes, Rhipicephalus).

Families—Gamasidae (Gamasus, Pteroptus).

Argasidae (Argas, Ornithodoros).

Ixodidae (Ixodes, Rhipicephalus).

Sub-orderd.Prostigmata.—Integument soft, strengthened by special sclerites, those on the ventral surface of the prosoma apparently representing the basal segments of the legs embedded in the skin. Tracheae, except in the aquatic species in which they are atrophied, opening by a pair of stigmata situated close to or above the base of the appendages of the 1st pair (mandibles).

Families—Trombidiidae (Trombidium, Tetranychus).Hydrachnidae (Hydrachna, Atax).Halacaridae (Halacarus, Leptognathus).Bdellidae (Bdella, Eupodes).

Families—Trombidiidae (Trombidium, Tetranychus).

Hydrachnidae (Hydrachna, Atax).

Halacaridae (Halacarus, Leptognathus).

Bdellidae (Bdella, Eupodes).

A, Lateral view with appendages III to VI removed; 1, plate covering the whole dorsal area, representing the fused tergal sclerites of the prosoma and opisthosoma; 2, similarly-formed ventral plate; 3, tracheal stigma.

B, Dorsal view of the same animal; II to VI, 2nd to 6th pairs of appendages. The 1st pair of appendages both in this and in C are retracted.

C, Ventral view of the same; II to VI as in B;a, genital orifice;b, anus;c, united basal segments of the second pair of appendages;d, basal segment of the 6th prosomatic appendage of the right side. The rest of the appendage, as also of app. Ill, IV and V, has been cut away.

Sub-ordere.Astigmata.—Degenerate, mostly parasitic forms approaching the Prostigmata in the development of integumental sclerites and the softness of the skin, but with the respiratory system absent.

Families—Tyroglyphidae (Tyroglyphus, Rhizoglyphus).Sarcoptidae (Sarcoptes, Analges).

Families—Tyroglyphidae (Tyroglyphus, Rhizoglyphus).

Sarcoptidae (Sarcoptes, Analges).

Sub-orderf.Vermiformia.—Degenerate atracheate parasitic forms with the body produced posteriorly into an annulated caudal prolongation, and the 3rd, 4th, 5th and 6th pairs of appendages short and only three-jointed.

Family—Demodicidae (Demodex).

Family—Demodicidae (Demodex).

Sub-orderg.Tetrapoda.—Degenerate atracheate gall-mites in which the body is produced posteriorly and annulated, as inDemodex, but in which the appendages of the 3rd and 4th pairs are long and normally segmented and those of the 5th and 6th pairs entirely absent.

Family—Eriophyidae (Eriophyes, Phyllocoptes).

Family—Eriophyidae (Eriophyes, Phyllocoptes).

Remarks on the Rhynchostomi.—The Acari include a number of forms which are of importance and special interest on account of their parasitic habits. The ticks (Ixodes) are not only injurious as blood-suckers, but are now credited with carrying the germs of Texas cattle-fever, just as mosquitoes carry those of malaria. The itch-insect (Sarcoptes scabiei) is a well-known human parasite, so minute that it was not discovered until the end of the 18th century, and “the itch” was treated medicinally as a rash. The female burrows in the epidermis much as the female trap-door spider burrows in turf in order to make a nest in which to rear her young. The male does not burrow, but wanders freely on the surface of the skin.Demodex folliculorumis also a common parasite of the sebaceousglands of the skin of the face in man, and is frequent in the skin of the dog. Many Acari are parasitic on marine and freshwater molluscs, and others are found on the feathers of birds and the hair of mammals. Others have a special faculty of consuming dry, powdery vegetable and animal refuse, and are liable to multiply in manufactured products of this nature, such as mouldy cheese. A species of Acarus is recorded as infesting a store of powdered strychnine and feeding on that drug, so poisonous to larger organisms. Reference to literature (40).

Authoritiescited by numbers in the text.—1. Strauss-Dürckheim (as reported by MM. Riester and Sanson in an appendix to the sixth volume of the French translation of Meckel’sAnatomy, 1829);2. Lankester, “Limulus an Arachnid,”Quart. Journ. Micr. Sci.vol. xxi. N.S., 1881;3.Idem, “On the Skeletotrophic Tissues of Limulus, Scorpio and Mygale,”Quart. Journ. Micr. Sci.vol. xxiv. N.S., 1884;4.Idem. Trans. Zool. Soc.vol. xi., 1883;5. Lankester and A.G. Bourne, “Eyes of Limulus and Scorpio,”Quart. Journ. Micr. Sci.vol. xxiii. N.S., Jan. 1883;6. Milne-Edwards, A., “Recherches sur l’anatomie des Limules,”Ann. Sci. Nat.5th Series,Zoologie, vol. xvii., 1873;7. Owen, Richard, “Anatomy of the King-Crab,”Trans. Linn. Soc. Lond., vol. xxviii., 1872;8. Kishinouye, “Development ofLimulus longispina,”Journal of the Science College of Japan, vol. v., 1892;9. Brauer, “Development of Scorpion,”Zeitschrift für wiss. Zoologie, vol. lix., 1895;10. Hansen, H.J., “Organs and Characters in Different Orders of Arachnida,”Entomol. Meddel.vol. iv. pp. 137-149;11. Watase, “On the Morphology of the Compound Eyes of Arthropods,”Studies from the Biolog. Lab. Johns Hopkins University, vol. iv. pp 287-334;12. Newport, George, “Nervous and Circulatory Systems in Myriapoda and Macrourous Arachnids,”Phil. Trans. Roy. Soc., 1843;13. Lankester, “Coxal Glands of Limulus, Scorpio and Mygale,”Quart. Journ. Micr. Sci.vol. xxiv. N.S., 1884;13A. W. Patten and A.P. Hazen, “Development of the Coxal Glands of Limulus,”Journ. of Morphology, vol. xvi., 1900; 13B. Bernard, “Coxal Glands of Scorpio,”Ann. and Mag. Nat. Hist.vol. xii., 1893, p. 55;14. Benham, “Testis of Limulus,”Trans. Linn. Soc., 1882;15. Lankester, “Mobility of the Spermatozoa of Limulus,”Quart. Journ. Micr. Sci.vol. xviii. N.S., 1878;16. Korschelt and Heider,Entwickelungsgeschichte(Jena, 1892),ibique citata;17. Laurie, M., “The Embryology of a Scorpion,”Quart. Journ. Micr. Sci.vol. xxxi. N.S., 1890, and “On Development ofScorpio fulvipes,”ibid.vol. xxxii., 1891;18. Lankester (Homoplasy and Homogeny), “On the Use of the term Homology in Modern Zoology,”Ann. and Mag. Nat. Hist., 1870;19.Idem, “Degeneration, a Chapter in Darwinism,” 1878, reprinted in theAdvancement of Science(Macmillan, 1890);20.Idem, “Limulus an Arachnid,”Q. J. Micr. Sci.vol. xxi. N.S.;21. Claus, “Degeneration of the Acari and Classification of Arthropoda,”Anzeiger d. k. k. Akad. Wissen. Wien, 1885; see alsoAnn. and Mag. Nat. Hist.(5) vol. xvii., 1886, p. 364, and vol. xix. p. 225;22. Lindstrom, G., “Researches on the Visual Organs of the Trilobites,”K. Svenska Vet. Akad. Handl.xxxiv. No. 8, pp. 1-86, Pls. i.-vi., 1901;22*. Zittel, American edition of hisPalaeontology(the Macmillan Co., New York), where ample references to the literature of Trilobitae and Eurypteridae will be found; also references to literature of fossil Scorpions and Spiders;23. Hoek, “Report on the Pycnogonida,”Challenger Expedition Reports, 1881; Meinert, “Pycnogonida of the Danish Ingolf Expedition,” vol. iii., 1899; Morgan, “Embryology and Phylogeny of the Pycnogonids,”Biol. Lab. Baltimore, vol. v., 1891;24. Bourne, A.G., “The Reputed Suicide of the Scorpion,”Proc. Roy. Soc.vol. xlii. pp. 17-22;25. Lankester, “Notes on some Habits of Scorpions,”Journ. Linn. Soc. Zool.vol. xvi. p. 455, 1882;26. Huxley, “Pharynx of Scorpion,”Quart. Journ. Micr. Sci.vol. viii. (old series), 1860, p. 250;27. Pocock, “How and Why Scorpions hiss,”Natural Science, vol. ix., 1896; cf.idem, “Stridulating Organs of Spiders,”Ann. and Mag. Nat. Hist.(6), xvi. pp. 230-233;28. Kraepelin,Das Thierreich (Scorpiones et Pedipalpi) (Berlin, 1899); Peters, “Eine neue Eintheilung der Skorpione,”Man. Akad. Wiss. Berlin, 1861; Pocock, “Classification of Scorpions,”Ann. and Mag. Nat. Hist.(6) xii., 1893; Thorell and Lindstrom, “On a Silurian Scorpion,”Kongl. Svens. Vet. Akad. Handl.xxi. No. 9, 1885;29. Cambridge, O.P., “A New Family (Tartarides) and Genus of Thelyphonidea,”Ann. and Mag. Nat. Hist.(4) x., 1872, p. 413; Cook, “Hubbardia, a New Genus of Pedipalpi,”Proc. Entom. Soc. Washington, vol. iv., 1899; Thorell, “Tartarides, &c.”Ann. Mus. Genova, vol. xxvii., 1889;30. M Cook,American Spiders and their Spinning Work(3 vols.; Philadelphia, 1889-1893);31. Peckham, “On Sexual Selection in Spiders,”Occasional Papers Nat. Hist. Soc. Wisconsin, vol. i. pp. 1-113, 1889;32. Moggridge,Harvesting Ants and Trap-Door Spiders(1873);33. Bertkau, Ph.,Arch. f. Naturgesch.vol. xlviii. pp. 316-362;Idem, same journal, 1875, p. 235, and 1878, p. 351; Cambridge, O.P., “Araneidea” inBiologia Centr. Americana, vols. i. and ii. (London, 1899); Keyserling,Spinnen Amerikas(Nuremberg, 1880-1892); Pocock, “Liphistius and the Classification of Spiders,”Ann. and Mag. Nat. Hist.(6) x., 1892; Simon,Hist. nat. des Araignées, vols. i. and ii., 1892, 1897; Wagner, “L’Industrie des Araneína,”Mem. Acad. St-Pétersbourg;Idem, “La Mue des Araignées,”Ann. Sci. Nat.vol. vi.;34. Grassi, G.B. “Intorno ad un nuovo Aracnide artrogastro (Koenenia mirabilis) &c.”Boll. Soc. Ent. Ital.vol. xviii., 1886;35. H.J. Hansen and Sörensen, “The Order Palpigradi, Thorell (Koenenia), and its Relationships with other Arachnida,”Ent. Tidskr.vol. xviii. pp. 233-240, 1898; Kraepelin,Das Thierreich(Berlin, 1901);36. Bernard. “Compar. Morphol. of the Galeodidae,”Trans. Linn. Soc. Zool.vol. vi., 1896,ibique citata; Dufour, “Galeodes,”Mém. prés. Acad. Sci. Paris, vol. xvii., 1862; Kraepelin,Das Thierreich(Berlin, 1901); Pocock, “Taxonomy of Solifugae,”Ann. and Mag. Nat. Hist.vol. xx.;37. Balzan, “Voyage au Vénézuela (Pseudoscorpiones),”Ann. Soc. Entom. France, 1891, pp. 497-522;38. Guérin-Méneville,Rev. Zool., 1838, p. II; Karsch, “Ueber Cryptostemma Guer.”Berliner entom. Zeitschrift, xxxviii. pp. 25-32, 1892; Thorell, “On an apparently new Arachnid belonging to the familyCryptostemmidae,”Westv. Bihang Svenska Vet. Akad. Handligar, vol. xvii. No. 9, 1892;39. Hansen and Sorensen,On Two Orders of Arachnida(Cambridge, 1904); Sörensen, “Opiliones laniatores,”Nat. Tidskr.(3) vol. xiv., 1884; Thorell, “Opilioni,”Ann. Mus. Genova, vol. viii., 1876;40. Berlese, “Acari, &c., in Italia reperta” (Padova, 1892); Canestrini,Acarofauna Italiana(Padova, 1885); Canestrini and Kramer, “Demodicidae and Sarcoptidae” inDas Thierreich(Berlin, 1899); Michael, “British Oribatidae,”Ray Soc.;Idem, “Oribatidae” inDas Thierreich(Berlin, 1898);Idem, “Progress and Present State of Knowledge of Acari,”Journ. Roy. Micr. Soc., 1894; Nalepa, “Phytoptidae,”Das Thierreich(Berlin, 1898); Trouessart, “Classification des Acariens,”Rev. Sci. Nat. de l’ouest.p. 289, 1892; Wagner,Embryonal Entwick, von Ixodes(St Petersburg, 1803);41. Bertkau, Ph., “Coxaldrusen der Arachniden,”Sitzb. Niederl. Gesellsch., 1885;42. Patten, W., “Brain and Sense Organs of Limulus,”Quart. Journ. Mic. Sci.vol. xxxv., 1894; see also his “Origin of Vertebrates from Arachnids,”ibid.vol. xxxi.

Authorities not cited by numbers in the text:—

Lung-books:—Berteaux, “Le Poumon des Arachnides,”La Cellule, vol. v. 1891; Jawarowski, “Die Entwick. d. sogen. Lunge bei der Arachniden,”Zeitsch. wiss. Zool.vol. lviii., 1894; Macleod, “Recherches sur la structure et la signification de l’appareil respiratoire des Arachnides,”Arch. d. Biologie.vol. v., 1884; Schneider, A., “Mélanges arachnologiques,” inTablettes zoologiques, vol. ii. p. 135, 1892; Simmons, “Development of Lung in Spiders,”Amer. Journ. Science, vol. xlviii., 1894.Coxal Glands:—Bertkau, “Ueber die Coxaldrusen der Arachniden,”Sitzb. d. Niederl. Gesellsch., 1885; Loman, “Altes und neues über das Nephridium (die Coxaldrüse) der Arachniden,”Bÿd. tot de Dierkunde, vol. xiv., 1887; Macleod, “Glande coxale chez les Galéodes,”Bull. Acad. Belg.(3) vol. viii., 1884; Pelseneer, “On the Coxal Glands of Mygale,”Proc. Zool. Soc., 1885; Tower, “The External Opening of the brick-red Glands of Limulus,”Zool. Anzeiger, vol. xviii. p. 471, 1895.Ento-sternite:—Schimkewitsch, “Bau und Entwick. des Endosternites der Arachniden,”Zool. Jahrb., Anal. Abtheil., vol. viii., 1894.Embryology:—Balfour, “Development of the Araneina,”Q. J. Micr. Sci.vol. xx., 1880; Kingsley, “The Embryology of Limulus,”Journ. Morphology, vols. vii. and viii.; Kishinouye, “Development of Araneina,”Journ. Coll. Sci. Univ. of Japan, vol. iv., 1890; Locy, “Development of Agelena,”Bull. Mus. Harvard, vol. xii., 1885; Metchnikoff, “Embryologie d. Scorpion,”Zeit. wiss. Zool.vol. xxi., 1871;Idem, “Embryol. Chelifer,”Zeit. wiss. Zool.vol. xxi., 1871; Schimkewitsch, “Développement des Araignées,”Archives d. Biologie, vol. vi. 1887.Sense organs:—Bertkau, “Sinnesorgane der Spinnen,”Arch. f. mikros. Anat.vol. xxvii. p. 589, 1886; Graber, “Unicorneale Tracheaten Auge,”Arch. f. mikr. Anat.vol. xvii., 1879; Grenacher,Gehörorgane der Arthropoden(Göttingen, 1879); Kishinouye, “Lateral Eyes of Spiders,”Zool. Anz.vol. xiv. p. 381, 1891; Purcell, “Phalangiden Augen,”Zool. Anzeiger, vol. xv. p. 461.

General works on Arachnida:—Blanchard, “Les Arachnides” inL’Organisation du regne animal; Gaubert, “Recherches sur les Arachnides,”Ann. Sci. Nat.(7) vol. xiii., 1892; Koch, C.,Die Arachniden(16 vols., Nuremberg, 1831-1848); Koch, Keyserling and Sörensen,Die Arachniden Australiens(Nuremberg, 1871-1890); Pocock,Arachnida of British India(London, 1900);Idem, “On African Arachnida,” inProc. Zool. Soc.andAnn. and Mag. Nat. Hist., 1897-1900; Simon,Les Arachnides de la France(7 vols., Paris, 1874-1881); Thorell, “Arachnida from the Oriental Region,”Ann. Mus. Genova, 1877-1899.

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