(2) Inserted a little dorsal to the transverse band just described is a second band which immediately crosses the first, and then passes on the outer side of the nervous cord and salivary gland, where such is present, and is inserted ventrally in the space between the ventro-lateral and lateral longitudinal band.
Where the feet are given off the second transverse band becomes continuous with the main retractor muscular fibres in the foot, which are inserted both on to the dorsal side and ventral side.
Muscular system of the feet.—This consists of the retractors of the feet connected with the outer transverse muscle and the circular layer of muscles. In addition to these muscles there are intrinsic transverse muscles which cross the cavity of the feet in various directions (Pl.51, fig. 20). There is no special circular layer of fibres.
Histology of the muscle.—The main muscles of the body are unstriated and divided into fibres, each invested by a delicate membrane. Between the membrane and muscle are scattered nuclei, which are never found inside the muscle fibres. The muscles attached to the jaws form an exception in that they are distinctly transversely striated.
The body-cavity, as already indicated, is formed of three compartments—one central and two lateral. The former is by far the largest, and contains the alimentary tract, the generative organs, and the mucous glands. It is lined by a delicate endothelial layer, and is not divided into compartments nor traversed by muscular fibres.
The lateral divisions are much smaller than the central, and are shut off from it by the inner transverse band of muscles. They are almost entirely filled with the nerve-cord and salivary gland in front and with the nerve-cord alone behind, and their lumen is broken up by muscular bands. They further contain the segmental organs which open into them. They are prolonged into the feet, as is the embryonic body-cavity of most Arthropoda.
The vascular system is usually stated to consist of a dorsal heart. I find between the dorsal bands of longitudinal fibres a vessel in a space shut off from the body-cavity by a continuation of the endothelial lining of the latter (fig. 16). The vessel has definite walls and an endothelial lining, but I could not make out whether the walls were muscular. The ventralpart of it is surrounded by a peculiar cellular tissue, probably, as suggested by Moseley, equivalent to the fat bodies of insects. It is continued from close to the hind end of the body to the head, and is at its maximum behind. In addition to this vessel there is present a very delicate ventral vessel, by no means easy to see, situated between the cutis and the outer layer of circular muscles.
A series of glandular organs are found in Peripatus which have their external openings situated on the ventral surface of a certain number of the legs, and which, to the best of my belief, end internally by opening into the lateral compartments of the body-cavity. These organs are probably of an excretory nature, and I consider them homologous with the nephridia or segmental organs of the Chætopoda.
InPeripatus capensisthey are present in all the legs. In all of them (except the first three) the following parts may be recognized:
(1) A vesicular portion opening to the exterior by a narrow passage.
(2) A coiled portion, which is again subdivided into several sections.
(3) A terminal section ending by a somewhat enlarged opening into the lateral compartment of the body-cavity.
The last twelve pairs of these organs are all constructed in a very similar manner, while the two pairs situated in the fourth and fifth pairs of legs are considerably larger than those behind, and are in some respects very differently constituted.
It will be convenient to commence with one of the hinder nephridia. Such a nephridium from the ninth pair of legs is represented in fig. 28. The external opening is placed at the outer end of a transverse groove placed at the base of one of the feet, while the main portion of the organ lies in the body-cavity in the base of the leg, and extends into the trunk to about the level of the outer edge of the nerve-cord of its side. The external opening (os) leads into a narrow tube (sd), which gradually dilates into a large sack (s).
The narrow part is lined by small epithelial cells, which are directly continuous with and perfectly similar to those of the epidermis (fig. 20). It is provided with a superficial coating of longitudinal muscular fibres, which thins out where it passes over the sack, along which it only extends for a short distance.
The sack itself, which forms a kind of bladder or collecting vesicle for the organ, is provided with an extremely thin wall, lined with very large flattened cells. These cells are formed of granular protoplasm, and each of them is provided with a large nucleus, which causes a considerable projection into the lumen of the sack (figs. 20, 29,s). The epithelial wall of the sack is supported by a membrana propria, over which a delicate layer of the peritoneal epithelium is reflected.
The coiled tube forming the second section of the nephridium varies in length, and by the character of the epithelium lining it may be divided into four regions. It commences with a region lined by a fairly columnar epithelium with smallish nuclei (fig. 28,sc1). The boundaries of the cells of this epithelium are usually very indistinct, and the protoplasm contains numerous minute granules, which are usually arranged in such a manner as to give to optical or real sections of the wall of this part of the tube a transversely striated appearance. These granules are very probably minute balls of excretory matter.
The nuclei of the cells are placed near their free extremities, contrary to what might have been anticipated, and the inner ends of the cells project for very different lengths into the interior, so causing the inner boundary of the epithelium of this part of the tube to have a very ragged appearance. This portion of the coiled tube is continuous at its outer end with the thin-walled vesicle. At its inner end it is continuous with regionNo.2 of the coiled tube (fig. 28,sc2), which is lined by small closely-packed columnar cells. This portion is followed by regionNo.3, which has a very characteristic structure (fig. 28sc3). The cells lining this part are very large and flat, and contain large disc-shaped nuclei, which are usually provided with large nucleoli, and often exhibit a beautiful reticulum. They may frequently be observed in a state of division. The protoplasm of this region is provided with similar granules to that in the first region, and the boundaries of the cells are usuallyvery indistinct. The fourth region is very short (fig. 28,sc4), and is formed of small columnar cells. It gradually narrows till it opens suddenly into the terminal section (sot), which ends by opening into the body-cavity, and constitutes the most distinct portion of the whole organ. Its walls are formed of columnar cells almost filled by oval nuclei, which absorb colouring matters with very great avidity, and thus renders this part extremely conspicuous. The nuclei are arranged in several rows.
The study of the internal opening of this part gave me some trouble. No specimens ever shew it as rounded off in the characteristic fashion of tubes ending in a cul-de-sac. It is usually somewhat ragged and apparently open. In the best preserved specimens it expands into a short funnel-shaped mouth, the free edge of which is turned back. Sections confirm the results of dissections. Those passing longitudinally through the opening prove its edges are turned back, forming a kind of rudimentary funnel. This is represented in fig. 29, from the last leg of a female. I have observed remains of what I consider to be cilia in this section of the organ. The fourth region of the organ is always placed close to the thin-walled collecting vesicle (figs. 28 and 29). In the whole of the coiled tube just described the epithelium is supported by a membrana propria, which in its turn is invested by a delicate layer of peritoneal epithelium.
The fourth and fifth pairs are very considerably larger than those behind, and are in other respects peculiar. The great mass of each organ is placed behind the leg, on which the external opening is placed, immediately outside one of the lateral nerve-cords. Its position is shewn in fig. 8.
The external opening, instead of being placed near the base of the leg, is placed on the ventral side of the third ring (counting from the outer end) of the thicker portion of the leg. It leads (fig. 27) into a portion which clearly corresponds with the collecting vesicle of the hinder nephridia. This part is not, however, dilated into a vesicle in the same sort of way, and the cells which form the lining epithelium have not the same characteristic structure, but are much smaller. Close to the point where the vesicle joins the coiled section of the nephridium theformer has a peculiar nick or bend in it. At this nick it is firmly attached to the ventral side of the foot by muscles and tracheæ, and when cut away from its attachment the muscles and tracheæ cannot easily be detached from it. The main part of the coils are formed by regionNo.1, and the epithelial cells lining this part present very characteristically the striated appearance which has already been spoken of. The large-celled region of the coiled tube (fig. 27) is also of considerable dimensions, and the terminal portion is wedged in between this and the commencing part of the coiled tube. The terminal portion with its internal opening is in its histological characters exactly similar to the homologous region in the hinder nephridia.
The three pairs of nephridia in the three foremost pairs of legs are very rudimentary, consisting, so far as I have been able to make out, solely of the collecting vesicle and the duct leading from them to the exterior. The external opening is placed on the ventral side of the base of the feet, in the same situation as that of the posterior nephridia, but the histological characters of the vesicle are similar to those of the fourth and fifth pairs.
[The sexes are distinct, and the average size of the females appears to be greater than that of the males.
The only outward characteristic by which the males can be distinguished from the females is the presence in the former of a small white papilla on the ventral side of the 17th pair of legs (Pl.47, fig. 4). At the extremity of this papilla the modified crural gland of the last leg opens by a slit-like aperture.
The generative orifice in both sexes is placed on the ventral surface of the body, close to the anus, and between the two anal papillæ, which are much more marked in small specimens than in large ones, and in two cases (of females) were observed to bear rudimentary claws.
1.The Male Organs.Pl.53, fig. 43.
The male organs consist of a pair of testes (te), a pair of prostrates (pr) and vasa deferentia (vd) and accessory glandular tubules (f).
All the above parts lie in the central compartment of the body-cavity. In addition, the accessory glandular bodies or crural glands of the last (17th) pair of legs[TN22]are enlarged and prolonged into an elongated tube placed in the lateral compartment of the body-cavity (ag).
The arrangement of these parts represented in the figure appears essentially that which Moseley has already described for this species. The dilatations on the vasa deferentia, which he calls vesiculæ seminales, is not so marked; nor can the peculiar spiral twisting of this part of the vas deferens which he figures (No.13) be made out in this specimen. The testes are placed at different levels in the median compartment of the body-cavity, and both lie on the same side of the intestine (right side).
The arrangement of the terminal portions of the vas deferens is precisely that described by Moseley. The right vas deferens passes under both nerve-cords to join the left, and from the enlarged tube (p), which, passing beneath the nerve-cord of its side, runs to the external orifice. The enlarged terminal portion possesses thick muscular walls, and possibly constitutes a spermatophore maker, as has been shewn to be the case in P. N. Zealandiæ, by Moseley.
In some specimens a different arrangement obtains, in that the left vas deferens passes under both nerve-cords to join the right.
In addition to the above structures, which are all described by Moseley, there are a pair of small glandular tubes (f), which open with the unpaired terminal portion of the vas deferens at the generative orifice.
2.Female Organs.Pl.52, fig. 33.
The female organs consist of a median unpaired ovary and a pair of oviducts, which are dilated for a great part of their course to perform a uterine function, and which open behind into a common vestibule communicating directly with the exterior.
Ovary.—In the specimen figured the following is the arrangement:
The ovary lies rather to the dorsal side in the central compartment of the body-cavity, and is attached to one of thelongitudinal septa separating this from the lateral compartment. It lies between the penultimate and antepenultimate pair of legs.
The oviducts cross before opening to the exterior. The right oviduct passes under the rectum, and the left over the rectum. They meet by opening into a common vestibule, which in its turn opens to the exterior immediately ventral to the anus. It has not been ascertained how far this arrangement, which differs from that observed by Moseley, is a normal one. The young undergo nearly the whole of their development within the uterus. They possess at birth the full number of appendages, and differ from the parent only in size and colour.]
1. They are present in all except the first.
2. They open externally to the nephridia (Pl.51, fig. 20), except in the fourth and fifth pairs of legs, in which they are internal.
3. A muscular layer covers the whole gland, consisting, I believe, of an oblique circular layer.
4. The accessory gland in the male (fig. 43,ag) is probably a modification of one of these organs.
[The structure and relations of these glands may be best understood by reference toPl.51, fig. 20. Each consists of a dilated vesicular portion (fgl) placed in the lateral compartment of the body-cavity in the foot, and of a narrow duct leading to the exterior, and opening on the ventral surface amongst the papillæ of the second row (counting from the internal of the three foot pads—fig. 20,P).
The vesicular portion is lined by columnar cells, with very large oval nuclei, while the duct is lined by cells similar to the epidermic cells, with which they are continuous at the opening.
In the last (17th) leg of the males of this species, this gland (videabove, note 4) possesses a slit-like opening placed at theapex of a well-developed white papilla (Pl.47, fig. 4). It is enormously enlarged, and is prolonged forward as a long tubular gland, the structure of which resembles that of the vesicles of the crural glands in the other legs. This gland lies in the lateral compartment of the body-cavity, and extends forward to the level of the 9th leg (Pl.48, fig. 8, andPl.53, fig. 43). It is described by Professor Balfour as the accessory gland of the male, and is seen in section lying immediately dorsal to the nerve-cord in fig. 20,ag.]
[570]Some material for this memoir was left by Prof. Balfour, which will be published separately.
[571]VideSpengel,“Oligognathus Bonelliæ."”Naples Mittheilungen,Bd.III.pl.IV.fig. 52.
[The remarkable discoveries about the early development of Peripatus, which Balfour made in June last, shortly before starting for Switzerland, have already been the subject of a short communication to the Royal Society (Proc. Roy. Soc.No.222, 1882). They relate (1) to the blastopore, (2) to the origin of the mesoblast.
Balfour left no manuscript account or notes of his discovery in connection with the drawings which he prepared in order to illustrate it, but he spoke about it to Professor Ray Lankester and also to us, and he further gave a short account of the matter in a private letter to Professor Kleinenberg.
In this letter, which by the courtesy of Professor Kleinenberg we have been permitted to see, he describes the blastopore as an elongated slit-like structure extending along nearly the whole ventral surface; and further states, as the result of his examination of the few and ill-preserved embryos in his possession, that the mesoblast appears to originate as paired outgrowths from the lips of the blastopore.
The drawings left by Balfour in connection with the discoveries are four in number: one of the entire embryo, shewing the slit-like blastopore and the mesoblastic somites, the other three depicting the transverse sections of the same embryo.
The first drawing (fig. 37),viz.that of the whole embryo, shews an embryo of an oval shape, possessing six somites, whilst along the middle of its ventral surface there are two slit-like openings, lying parallel to the long axis of the body, and placed one behind the other. The mesoblastic somites are arranged bilaterally in pairs, six on either side of these slits. The following note in his handwriting is attached to this drawing:
“Young larva ofPeripatus capensis.—I could not make out for certain which was the anterior end. Length 1.34 millimetres.”
Balfour's three remaining drawings (figs. 40-42) are, as already stated, representations of transverse sections of the embryo figured by him as a whole. They tend to shew, as he stated in the letter referred to above, that the mesoblast originates as paired outgrowths from the hypoblast, and that these outgrowths are formed near the junction of the hypoblast with the epiblast at the lips of the blastopore.
In fig. 42 the walls of the mesoblastic somites appear continuous with those of the mesenteron near the blastopore.
In fig. 40, which is from a section a little in front of fig. 42, the walls of the mesoblastic somites are independent of those of the mesenteron.
Fig. 41 is from a section made in front of the region of the blastopore.
In all the sections the epiblast lying over the somites is thickened, while elsewhere it is formed of only one layer of cells; and this thickening subsequently appears to give rise to the nervous system. Balfour in his earlier investigations on the present subject found in more advanced stages of the embryo the nerve-cords still scarcely separated from the epiblast[572].
We have since found, in Balfour's material, embryos of a slightly different age to that just described. Of these, three (figs. 34, 35, 36) are younger, while one (fig. 38) is older than Balfour's embryo.
Stage A.—The youngest (fig. 34) is of a slightly oval form, and its greatest length is .48mm.It possesses a blastopore,which is elongated in the direction of the long axis of the embryo, and is slightly narrower in its middle than at either end. From one end of the blastopore there is continued an opaque band. This we consider to be the posterior end of the blastopore of the embryo. The blastopore leads into the archenteron.
Stage B.—In the next stage (fig. 35) the embryo is elongate-oval in form. Its length is .7mm.The blastopore is elongated and slightly narrowed in the middle. At the posterior end of the embryo there is a mass of opaque tissue. On each side of the blastopore are three mesoblastic somites. The length of the blastopore is .45mm.
Stage C.—In the next stage (fig. 36) the features are much the same as in the preceding. The length of the whole embryo is .9mm.
The following were the measurements of an embryo of this stage with five somites, but slightly younger than that from which fig. 36 was drawn.
The somites have increased to five, and there are indications of a sixth being budded off from the posterior mass of opaque tissue. The median parts of the lips of the blastopore have come together preparatory to the complete fusion by which the blastopore becomes divided into two parts.
Stage D.—The next stage is Balfour's stage, and has been already described.
The length is 1.34.
It will be observed, on comparing it with the preceding embryos, that while the anterior pair of somites in figs. 35 and 36 lie at a considerable distance from what we have called the anterior end of the embryo (a), in the embryo now under consideration they are placed at the anterior end of the body, one on each side of the middle line. We cannot speak positively as to how they come there, whether by a pushing forward ofthe anterior somites of the previous stage, or by the formation of new somites anteriorly to those of the previous stage.
In the next stage it is obvious that this anterior pair of somites has been converted into the præoral lobes.
The anterior of the two openings to which the blastopore gives rise is placed between the second pair of somites; we shall call it the embryonic mouth. The posterior opening formed from the blastopore is elongated, being dilated in front and continued back as a narrow slit (?) to very near the hind end of the embryo, where it presents a second slight dilatation. The anterior dilatation of the posterior open region of the blastopore we shall call the embryonic anus.
Lately, but too late to be figured with this memoir, we have been fortunate enough to find an embryo of apparently precisely the same stage as fig. 37. We are able, therefore, to give a few more details about the stage.
The measurements of this embryo were:
Stage E.—In the next stage (figs. 38 and 39) the flexure of the hind end of the body has considerably increased. The anterior opening of the blastopore, the embryonic mouth, has increased remarkably in size. It is circular, and is placed between the second pair of mesoblastic somites. The anterior dilatation of the posterior opening of the blastopore, the embryonic anus, has, like the anterior opening, become much enlarged. It is circular, and is placed on the concavity of the ventral flexure. From its hind end there is continued to the hind end of the body a groove (shewn in fig. 39 as a dotted line), which we take to be the remains of the posterior slit-like part of the posterior opening of the blastopore of the preceding stage. The posterior dilatation has disappeared. Theembryo has apparently about thirteen somites, which are still quite distinct from one another, and apparently do not communicate at this stage with the mesenteron.
The epiblast lying immediately over the somites is, as in the, earlier stages, thickened, and the thickenings of the two sides join each other in front of the embryonic mouth, where the anterior pair of mesoblastic somites (the præoral lobes) are almost in contact.
The median ventral epiblast,i.e.the epiblast in the area, bounded by the embryonic mouth and anus before and behind and by the developing nerve-cords laterally, is extremely thin, and consists of one layer of very flat cells. Over the dorsal surface of the body the epiblast cells are cubical, and arranged in one layer.
These measurements were made with a micrometer eyepiece, with the embryo lying on its back in the position of fig. 38, so that they simply indicate the length of the straight line connecting the respective points.
This is the last embryo of our series of young stages. The next and oldest embryo was 3.2mm.in length. It had ringed antennæ, seventeen (?) pairs of legs, and was completely doubled upon itself, as in Moseley's figure.
The pits into the cerebral ganglia and a mouth and anus were present. There can be no doubt that the mouth and anus of this embryo become the mouth and anus of the adult.
The important question as to the connection between the adult mouth and anus, and the embryonic mouth and anus of the Stage E, must, considering the great gap between Stage E and the next oldest embryo, be left open. Meanwhile, we may point out that the embryonic mouth of Stage E has exactly thesame position as that of the adult; but that the anus is considerably in front of the hind end of the body in Stage E, while it is terminal in the adult.
If the embryonic mouth and anus do become the adult mouth and anus, there would appear to be an entire absence of stomodæum and proctodæum inPeripatus, unless the buccal cavity represents the stomodæum. The latter is formed, as has been shewn by Moseley, by a series of outgrowths round the simple mouth-opening of the embryo, which enclosing the jaws give rise to the tumid lips of the adult.
For our determination of the posterior and anterior ends of each of these embryos, Stage A to E, we depend upon the opaque tissue seen in each case at one end of the blastopore.
In Stage A it has the form of a band, extending backwards from the blastopore.
In Stages B-D, it has the form of an opaque mass of tissue occupying the whole hind end of the embryo, and extending a short distance on either side of the posterior end of the blastopore.
This opacity is due in each case to a proliferation of cells of the hypoblast, and, perhaps, of the epiblast (?).
There can be no doubt that the mesoblast so formed gives rise to the great majority of the mesoblastic somites.
This posterior opacity is marked in Stage C by a slight longitudinal groove extending backwards from the hind end of the blastopore. This is difficult to see in surface views, and has not been represented in the figure, but is easily seen in sections.
But in Stage D this groove has become very strongly marked in surface views, and looks like a part of the original blastopore of Stage C.
Sections shew that it does not lead into the archenteron, but only into the mass of mesoblast which forms the posterior opacity. It presents an extraordinary resemblance to the primitive streak of vertebrates, and the ventral groove of insect embryos.
We think that there can be but little doubt that it is a part of the original blastopore, which, on account of its late appearance (this being due to the late development of the posteriorpart of the body to which it belongs), does not acquire the normal relations of a blastopore, but presents only those rudimentary features (deep groove connected with origin of mesoblast) which the whole blastopore of other tracheates presents.
We think it probable that the larval anus eventually shifts to the hind end of the body, and gives rise to the adult anus. We reserve the account of the internal structure of these embryos (Stages A-E) and of the later stages for a subsequent memoir.
We may briefly summarise the more important facts of the early development ofPeripatus capensis, detailed in the preceding account.
1. The greater part of the mesoblast is developed from the walls of the archenteron.
2. The embryonic mouth and anus are derived from the respective ends of the original blastopore, the middle part of the blastopore closing up.
3. The embryonic mouth almost certainly becomes the adult mouth,i.e.the aperture leading from the buccal cavity into the pharynx, the two being in the same position. The embryonic anus is in front of the position of the adult anus, but in all probability shifts back, and persists as the adult anus.
4. The anterior pair of mesoblastic somites gives rise to the swellings of the præoral lobes, and to the mesoblast of the head[573].
There is no need for us to enlarge upon the importance of these facts. Their close bearing upon some of the most important problems of morphology will be apparent to all, and we may with advantage quote here some passages from Balfour'sComparative Embryology, which shew that he himself long ago had anticipated and in a sense predicted their discovery.
“Although the mesoblastic groove of insects is not a gastrula, it is quite possible that it is the rudiment of a blastopore, the gastrula corresponding to which has now vanishedfrom development.”(Comparative Embryology,Vol.I.p. 378, the original edition[574].)
“Tracheata.—Insecta. It (the mesoblast) grows inwards from the lips of the germinal groove, which probably represents the remains of a blastopore.”(Comparative Embryology,Vol.II.p. 291, the original edition[575].)
“It is, therefore, highly probable that the paired ingrowths of the mesoblast from the lips of the blastopore may have been, in the first instance, derived from a pair of archenteric diverticula.”(Comparative Embryology,Vol.II.p. 294, the original edition[576].)
The facts now recorded were discovered in June last, only a short time before Balfour started for Switzerland; we know but little of the new ideas which they called up in his mind. We can only point to passages in his published works which seem to indicate the direction which his speculations would have taken.
After speculating as to the probability of a genetic connection between the circumoral nervous system of the Cœlenterata, and the nervous system of Echinodermata, Platyhelminthes[TN23], Chætopoda, Mollusca,&c., he goes on to say:
“A circumoral nerve-ring, if longitudinally extended, might give rise to a pair of nerve-cords united in front and behind—exactly such a nervous system, in fact, as is present in many Nemertines (the Enopla and Pelagonemertes), inPeripatusand in primitive molluscan types (Chiton, Fissurella,&c.). From the lateral parts of this ring it would be easy to derive the ventral cord of the Chætopoda and Arthropoda. It is especially deserving of notice, in connection with the nervous system of the above mentioned Nemertines and Peripatus, that the commissure connecting the two nerve-cords behind is placed on the dorsal side of the intestines. As is at once obvious, by referring to the diagram (fig. 231B), this is the position this commissure ought, undoubtedly, to occupy if derived from part of a nerve-ring which originally followed more or less closely the ciliated edge of the body of the supposed radiate ancestor.”(Comparative Embryology,Vol.II.pp.311, 312, the original edition[577].)
The facts of development here recorded give a strong additional support to this latter view, and seem to render possible a considerable extension of it along the same lines.]
List of Memoirs on Peripatus.
1. M. LansdownGuilding.“An Account of a New Genus of Mollusca,”Zoological Journal,Vol.II.p. 443, 1826.
2. M.AndouinandMilne-Edwards.“Classific. des Annélides et description de celles qui habitent les côtes de France,”p. 411,Ann. Scien. Nat.ser.I.Vol.XXX.1833.
3. M.Gervais.“Études p. servir à l'histoire naturelle des Myriapodes,”Ann. Scien. Nat.ser.II.Vol.VII.1837, p. 38.
4.Wiegmann.Wiegmann'sArchiv, 1837.
5. H.Milne-Edwards.“Note sur lePeripate juluforme,”Ann. Scien. Nat.ser.II.Vol.XVIII.1842.
6.Blanchard.“Sur l'organisation des Vers,”chap. IV.pp.137-141,Ann. Scien. Nat.ser.III.Vol.VIII.1847.
7.Quatrefages.“Anat. des Hermelles, note on,”p. 57,Ann. Scien. Nat.ser.III.Vol.X.1848.
8.Quatrefages.Hist. Nat. des Annelés, 1865, Appendix,pp.675-6.
9. DeBlainville.Suppl. au Dict. des Sc. Nat.Vol.I.
10. Ed.Grube.“Untersuchungen üb. d. Bau vonPeripatus Edwardsii,”Archiv für Anat. und Physiol.1853.
11.Saenger.“Moskauer Naturforscher Sammlung,”Abth. Zool.1869.
12. H. N.Moseley.“On the Structure and Development ofPeripatus capensis,”Proc. Roy. Soc.No.153, 1874.
13. H. N.Moseley.“On the Structure and Development ofPeripatus capensis,”Phil. Trans.Vol.CLXIV.1874.
14. H. N.Moseley.“Remarks on Observations by Captain Hutton, Director of the Otago Museum, onPeripatus novæ zealandiæ,”Ann. and Mag. of Nat.History,Jan.1877.
15. CaptainHutton.“Observations onPeripatus novæ zealandiæ,”Ann. and Mag. of Nat.History,Nov.1876.
16. F. M.Balfour.“On Certain Points in the Anatomy ofPeripatus capensis,”Quart. Journ. of Micr.Science,Vol.XIX.1879.
17. A.Ernst.Nature, March 10th, 1881.
EXPLANATION OF PLATES 46-53[578].
Complete List of Reference Letters.
A.Anus.a.Dorso-lateral horn of white matter in brain.a.g.Accessory gland of male (modified accessory leg gland).at.Antenna.at.n.Antennary nerve.b.Ventro-lateral horn of white matter of brain.b.c.Body-cavity.bl.Blastopore.C.Cutis.c.Postero-dorsal lobe of white matter of brain.c.g.Supra-œsophageal ganglia.cl.Claw.c.m.Circular layer of muscles.co.Commissures between the ventral nerve-cords.co.2.Second commissure between the ventral nerve-cords.co1. 2. Mass of cells developed on second commissure.cor.Cornea.c.s.d.Common duct for the two salivary glands.cu.Cuticle.d.Ventral protuberance of brain.d.l.m.Dorsal longitudinal muscle of pharynx.d.n.Median dorsal nerve to integument from supra-œsophageal ganglia.d.o.Muscular bands passing from the ventro-lateral wall of the pharynx at the region of its opening into the buccal cavity.E.Eye.E.Central lobe of white matter of brain.e.n.Nerves passing outwards from the ventral cords.ep.Epidermis.ep.c.Epidermis cells.F.1,F.2,&c.First and second pair of feet,&c.f.Small accessory glandular tubes of the male generative apparatus.F.g.Ganglionic enlargement on ventral nerve-cord, from which a pair of nerves to foot pass off.f.gl.Accessory foot-gland.F.n.Nerves to feet.g.co.Commissures between the ventral nerve-cords containing ganglion cells.g.o.Generative orifice.H.Heart.h.Cells in lateral division of body-cavity.hy.Hypoblast.i.j.Inner jaw.j.Jaw.j.n.Nerves to jaws.L.Lips.l.Lens.l.b.c.Lateral compartment of body-cavity.le.Jaw lever (cuticular prolongation of inner jaw lying in a backwardly projecting diverticulum of the buccal cavity).l.m.Bands of longitudinal muscles.M.Buccal cavity.M1.Median backward diverticulum of mouth or common salivary duct which receives the salivary ducts.me.Mesenteron.mes.Mesoblastic somite.m.l.Muscles of jaw lever.m.s.Sheets of muscle passing round the side walls of pharynx to dorsal body-wall.od.Oviduct.œ. Œsophagus.œs.co.Œsophageal commissures.o.f.g.Orifice of duct of foot-gland.o.j.Outer jaw.op.Optic ganglion.op.n.Optic nerve.or.g.Ganglionic enlargements for oral papillæ.or.n.Nerves to oral papillæ.or.p.Oral papillæ.o.s.Orifice of duct of segmental organ.ov.Ovary.P.Pads on ventral side of foot.p.Common duct into which the vasa deferentia open.p.c.Posterior lobe of brain.p.d.c.Posterior commissure passing dorsal to rectum.p.f.Internal opening of nephridium into body-cavity.ph.Pharynx.pi.Pigment in outer ends of epidermic cells.pi.r.Retinal pigment.p.n.Nerves to feet.p.p.Primary papilla.pr.Prostate.R.Rectum.re.Retinal rods.R.m.Muscle of claw.s.Vesicle of nephridium.s1. Part of 4th or 5th nephridium which corresponds to vesicle of other nephridia.s.c.1. RegionNo.1 of coiled tube of nephridium.s.c.2. RegionNo.2 of ditto.s.c.3. RegionNo.3 of ditto.s.c.4. RegionNo.4 of ditto.s.d.Salivary duct.s.g.Salivary gland.sl.d.Reservoir of slime gland.sl.g.Tubules of slime gland.s.o.1, 2, 3,&c.Nephridia of 1st, 2nd,&c., feet.s.o.f.Terminal portion of nephridium.s.p.Secondary papilla.st.Stomach.st.e.Epithelium of stomach.sy.Sympathetic nerve running in muscles of tongue and pharynx.sy´. Origin of pharyngeal sympathetic nerves.T.Tongue.t.Teeth on tongue.te.Testis.tr.Tracheæ.tr.c.Cells found along the course of the tracheæ.tr.o.Tracheal stigma.tr.p.Tracheal pit.ut.Uterus.v.c.Ventral nerve cord.v.d.Vas deferens.v.g.Imperfect ganglia of ventral cord.
Plate 46.
Fig. 1.Peripatus capensis, x 4; viewed from the dorsal surface. (From a drawing by Miss Balfour.)
Plate 47.
Fig. 2. A left leg ofPeripatus capensis, viewed from the ventral surface; x 30. (From a drawing by Miss Balfour.)
Fig. 3. A right leg ofPeripatus capensis, viewed from the front side. (From a drawing by Miss Balfour.)
Fig. 4. The last left (17th) leg of a malePeripatus capensis, viewed from the ventral side to shew the papilla at the apex of which the accessory gland of the male, or enlarged crural gland, opens to the exterior. (From a drawing by Miss Balfour.) Prof. Balfour left a rough drawing (not reproduced) shewing the papilla, to which is appended the following note.“Figure shewing the accessory genital gland of male, which opens on the last pair of legs by a papilla on the ventral side. The papilla has got a slit-like aperture at its extremity.”
Fig. 5. Ventral view of head and oral region ofPeripatus capensis. (From a drawing by Miss Balfour.)
Plate 48.
Figs. 6 and 7 are from one drawing.
Fig. 6.Peripatus capensisdissected so as to shew the alimentary canal, slime glands, and salivary glands; x 3. (From a drawing by Miss Balfour.)
Fig. 7. The anterior end of Fig. 6 enlarged; x 6. (From a drawing by Miss Balfour.) The dissection is viewed from the ventral side, and the lips,L., have been cut through in the middle line behind and pulled outwards, so as to expose the jaws,j., which have been turned outwards, and the tongue,T., bearing a median row of chitinous teeth, which branches behind into two. The junction of the salivary ducts,s.d., and the opening of the median duct so formed into the buccal cavity is also shewn. The muscular pharynx, extending back into the space between the 1st and 2nd pairs of legs, is followed by a short tubular œsophagus. The latter opens into the large stomach with plicated walls, extending almost to the hind end of the animal. The stomach at its point of junction with the rectum presents anS-shaped ventro-dorsal curve.
A.Anus.at.Antenna.F.1,F.2. First and second feet.j.Jaws.L.Lips.œ. Œsophagus.or.p.Oral papilla.ph.Pharynx.R.Rectum.s.d.Salivary duct.s.g.Salivary gland.sl.d.Slime reservoir.sl.g.Portion of tubules of slime gland.st.Stomach.T.Tongue in roof of mouth.
Fig. 8.Peripatus capensis, x 4; male. (From a drawing by Miss Balfour.) Dissected so as to shew the nervous system, slime glands, ducts of the latter passing into the oral papilla, accessory glands opening on the last pair of legs (enlarged crural glands), and segmental organs, viewed from dorsal surface. The first three pairs of segmental organs consist only of the vesicle and duct leading to the exterior. The fourth and fifth pairs are larger than the succeeding, and open externally to the crural glands. The ventral nerve-cords unite behind dorsal to the rectum.
A.Anus.a.g.Accessory generative gland, or enlarged crural gland of the 17th leg.at.Antenna.c.g.Supra-œsophageal ganglia with eyes.co.Commissures between the ventral nerve-cords.d.n.Large median nerve to dorsal integument from hinder part of brain.F.1, 2,&c.Feet.g.o.Generative orifice.œ.Œsophagus.œs.co.Œsophageal commissures.or.p.Oral papilla.p.d.c.Posterior dorsal commissure between the ventral nerve-cords.ph.Pharynx.p.n.Nerves to feet, one pair from each ganglionic enlargement.sl.d.Reservoir of slime gland.sl.g.Tubules of slime gland.s.o.1, 2, 3,&c.Segmental organs.v.c.Ventral nerve-cords.v.g.Imperfect ganglia of ventral cords.
Figs. 9 and 10. Left jaw ofPeripatus capensis(male), shewing reserve jaws. (From a drawing by Miss Balfour.)
Fig. 9. Inner jaw.
Fig. 10. Outer jaw.
Plate 49.
Figs. 11-16. A series of six transverse sections through the head ofPeripatus capensis.
Fig. 11. The section is taken immediately behind the junction of the supra-œsophageal ganglia,c.g., and passes through the buccal cavity,M., and jaws,o.j.andi.j.
Fig. 12. The section is taken through the hinder part of the buccal cavity at the level of the opening of the mouth into the pharynx and behind the jaws. The cuticular rod-like continuation (le.) of the inner jaw lying in a backwardly directed pit of the buccal cavity is shewn; on the right hand side the section passes through the opening of this pit.
Fig. 13. The section passes through the front part of the pharynx, and shews the opening into the latter of the median backward diverticulum of the mouth (M1), which receives the salivary ducts. It also shews the commencement of the ventral nerve-cords, and the backwardly projecting lobes of the brain.
Fig. 14. The section passes through the anterior part of the pharynx at the level of the second commissure (co.2), between the ventral nerve-trunks, and shews the mass of cells developed on this commissure, which is in contact with the epithelium of the backward continuation of the buccal cavity (M1).
Fig. 15. Section through the point of junction of the salivary ducts with the median oral diverticulum.
Fig. 16. Section behind the pharynx through the œsophagus.
b.c.Body-cavity.C.Cutis.c.b.c.Central compartment of body-cavity.c.g.Supra-œsophageal ganglia.c.m.Layer of circular muscles.co.Commissure between ventral nerve-cords.co.2. Second commissure between the ventral nerve-cords.co1.2.Mass of cells developed on second commissure (probably sensory).c.s.d.Common duct for the two salivary glands.d.l.m.Dorsal longitudinal muscles of pharynx.d.o.Muscles serving to dilate the opening of the pharynx.Ep.Epidermis.e.n.Nerve passing outwards from ventral nerve-cord.H.Heart.i.j.Inner jaw.j.p.Jaw papillæ.L.Lips of buccal cavity.l.b.c.Lateral compartment of body-cavity.le.Rod-like cuticular continuation of inner jaw, lying in a pit of the buccal cavity.l.m.Bands of longitudinal muscles.M.Buccal cavity.M1. Median backward continuation of buccal cavity.m.l.Muscles of jaw lever.m.s.Muscular sheets passing from side walls of pharynx to dorsal body-wall.œ. Œsophagus.œs.co.Œsophageal commissures.o.j.Outer jaw.ph.Pharynx.s.d.Salivary duct.s.g.Salivary gland.sl.d.Reservoir of slime gland.sy.Sympathetic nerves running in muscles of tongue or pharynx.sy1.Origin of sympathetic nerves to pharynx.T.Tongue.v.c.Ventral nerve-cords.
Figs. 17, 18. Two longitudinal horizontal sections through the head ofPeripatus capensis. Fig. 17 is the most ventral. They are both taken ventral to the cerebral ganglia. In Fig. 17 dorsal tracheal pits are shewn with tracheæ passing off from them. (Zeiss a a, Hartnack's camera.)C.Cutis.c.s.d.Common salivary duct.ep.Epidermis.i.j.Inner jaw.M.Buccal cavity.M1. Median backward diverticulum of mouth.o.j.Outer jaw.s.d.Salivary ducts.T.Tongue.t.Teeth on tongue.tr.Tracheæ.tr.p.Tracheal pits.
Plate 50.
Fig. 19. "A, B, C, D, E, F, G." Seven transverse sections illustrating the structure of the supra-œsophageal ganglia. (Zeiss A, Hartnack's camera.)a.Dorso-lateral horn of white matter.b.Ventro-lateral horn of white matter.c.Postero-dorsal lobe of white matter.d.Ventral protuberance of brain.e.Central lobe of white matter.o.p.Optic ganglion.
“A.Section through anterior portions of ganglia close to the origin of the antennary nerve.B.Section a little in front of the point where the two ganglia unite.C.Section close to anterior junction of two ganglia.D.Section through origin of optic nerve on the right side.E.Section shewing origin of the optic nerve on the left side.F.Section through the dorso-median lobe of white matter.G.Section near the termination of the dorsal tongue of ganglion cells.”
Plate 51.
Fig. 20. Portion of a transverse section through the hinder part ofPeripatus capensis(male). The section passes through a leg, and shews the opening of the segmental organ (o.s.), and of a crural gland,o.f.g., and the forward continuation ofthe enlarged crural gland of the 17th leg (f.gl.). (Zeiss a a, Hartnack's camera.)a.g.accessory gland of male (modified crural gland of last leg).C.Cutis.cl.Claw.cu.Cuticle.ep.Epidermis.f.gl.Crural gland.h.Cells in lateral compartment of body-cavity.o.f.g.Orifice of accessory foot gland.o.s.Opening of segmental organ.P.Three spinous pads on ventral surface of foot.pr.Prostate.R.M.Retractor muscle of claw.s.Vesicle of nephridium.s.c.i.RegionNo.1 of coiled part of nephridium.sl.g.Tubule of slime gland.s.o.t.Terminal portion of nephridium.st.Stomach.st.e.Epithelium of stomach.v.c.Ventral nerve-cord.v.d.Vas deferens.
Fig. 21.“Longitudinal vertical section through the supra-œsophageal ganglion and œsophageal commissures ofPeripatus capensis. (Zeiss a a, Hartnack.)”at.Antenna.e.Central lobe of white matter.j.Part of jaw.s.g.Salivary gland.
Fig. 22: drawn by Miss Balfour. Brain and anterior part of the ventral nerve-cords ofPeripatus capensisenlarged and viewed from the ventral surface. The paired appendages (d) of the ventral surface of the brain are seen, and the pair of sympathetic nerves (sy1) arising from the ventral surface of the hinder part.
From the commencement of the œsophageal commissures (œs.co.) pass off on each side a pair of nerves to the jaws (j.n.).
The three anterior commissures between the ventral nerve-cords are placed close together; immediately behind them the nerve-cords are swollen, to form the ganglionic enlargements from which pass off to the oral papillæ a pair of large nerves on each side (or.n.).
Behind this the cords present a series of enlargements, one pair for each pair of feet, from which a pair of large nerves pass off on each side to the feet (p.n).at.n.Antennary nerves.co.Commissures between ventral cords.d.Ventral appendages of brain.E.Eye.e.n.Nerves passing outwards from ventral cord.F.g.Ganglionic enlargements from which nerves to feet pass off.j.n.Nerves to jaws.or.g.Ganglionic enlargement from which nerves to oral papillæ pass off.or.n.Nerves to oral papillæ.p.c.Posterior lobe of brain.p.n.Nerves to feet.s.y.Sympathetic nerves.
Fig. 23.“Longitudinal horizontal section through the head ofPeripatus capensis, shewing the structure of the brain, the antennary and optic nerves,&c.(Zeiss a a, Hartnack's camera.)”at.Antenna.at.n.Antennary nerve.cor.Cornea.e.Central mass of white matter.l.Lens.op.n.Optic nerve.ph.Pharynx.p.p.Primary papilla covered with secondary papillæ and terminating in a long spine.sy.Pharyngeal sympathetic nerves.
Fig. 24.“Eye ofPeripatus capensis, as shewn in a longitudinal horizontal section through the head. The figure is so far diagrammatic that the lens is represented as filling up the whole space between the rods and the cornea. In the actual section there is a considerable space between the parts, but this space is probably artificial, being in part caused by the shrinkage of the lens and in part by the action of the razor. (ZeissC, Hartnack's camera.)”(It appears that the ganglionic region of the eye is covered by a thin capsule, which is omitted in the figure.)
cor.Cornea.l.Lens.op.Optic ganglion.op.n.Optic nerve.pi.r.Pigment.Re.rods.s.p.Secondary papillæ.
Fig. 25. Longitudinal horizontal section through the dorsal skin, shewing the peculiar arrangement of the circular muscular fibres. (ZeissA, Hartnack's camera.)
Plate 52.
Fig. 26. Portion of ventral cord ofPeripatus capensisenlarged, shewing two ganglionic enlargements and the origin of the nerves and commissures. (From a drawing by Miss Balfour.)
co.Commissures.E.n.Nerves passing out from ventral cords.F.n.Nerves to feet.g.co.Commissures between the ventral cords containing ganglion cells.v.g.Ganglionic enlargements.
Fig. 27. Segmental organ from the 5th pair of legs ofPeripatus capensis. This nephridium resembles those of the 4th legs, and differs from all the others in its large size and in the absence of any dilatation giving rise to a collecting vesicle on its external portion (enlarged). The terminal portion has the same histological characters as in the case of the hinder segmental organs. (From a drawing by Miss Balfour.)
Fig. 28. Segmental organ or nephridium from the 9th pair of legs ofPeripatus capensis, shewing the external opening, the vesicle, the coiled portion and the terminal portion with internal opening (enlarged). (From a drawing by Miss Balfour.)
o.s.External opening of segmental organ.p.f.Internal opening of nephridium into the body-cavity (lateral compartment).s.Vesicle of segmental organ.s1. Portion of segmental organ of 4th and 5th legs, corresponding to vesicle of the other nephridia.s.c.1.First or external portion of coiled tube of nephridium, lined by columnar epithelium with small nuclei; the cells project for very different distances, giving the inner boundary of this region a ragged appearance.s.c.2. RegionNo.2 of coiled tube of nephridium, lined by small closely-packed columnar cells.s.c.3. RegionNo.3 of coiled tube of segmental organ, lined by large flat cells with large disc-shaped nuclei.s.c.4. RegionNo.4 of coiled tube of nephridium; this region is very short and lined by small columnar cells.s.o.t.Terminal portion of nephridium.
Fig. 29.“Portion of nephridium of the hindermost leg ofPeripatus capensis, seen in longitudinal and vertical section. The figure is given to shew the peritoneal funnel of the nephridium. Portions of the collecting sack (s.) and other parts are also represented. (ZeissB, Hartnack's camera.)”
p.f.Peritoneal funnel.s.Vesicle.s.c.1,s.c.2,s.c.3.Portions of coiled tube.
Fig. 30.“Section through a tracheal pit and diverging bundles of tracheal tubes”taken transversely to the long axis of the body. (ZeissE,oc.2.) (From a rough drawing by Prof. Balfour.)
tr.Tracheæ, shewing rudimentary spiral fibre.tr.c.Cells resembling those lining the tracheal pits, which occur at intervals along the course of the tracheæ.tr.s.Tracheal stigma.tr.p.Tracheal pit.
Fig. 31.“Sense organs and nerves attached from antenna ofPeripatus capensis(Zeiss, immersion 2,oc.2.)”(From a rough drawing by Prof. Balfour.) The figure shews the arrangement of the epidermis cells round the base of the spine. The spine is seen to be continuous with the inner layer of the cuticle.
Fig. 32. Section through the skin ofPeripatus capensis; it shews the secondary papillæ covered with minute spinous tubercles and the relation of the epidermis to them. (The cuticle in the process of cutting has been torn away from the subjacent cells.) The cells of the epidermis are provided with large oval nuclei, and there is a deposit of pigment in the outer ends of the cells. The granules in the protoplasm of the inner ends of the cells are arranged in lines, so as to give a streaked appearance. (ZeissE,oc.2.) (From a rough drawing by Prof. Balfour.)