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Library of the Museum OF ‘COMPARATIVE ZOOLOGY,

AT HARVARD COLLEGE, CAMBRIDGE, MASS.

Pounded by private subscription, in 1861.

Deposited by ALEX. AGASSIZ.

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QUARTERLY JOURNAL

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EDITED BY

E. RAY LANKESTER, M.A., LL.D., F.RB.S.,

Honorary Fellow of Exeter College, Oxford ; Jodrell Professor of Zoology in University College, London; and Deputy Linacre Professor of Human and Comparative Anatomy in the University of Oxford.

WITH THE CO-OPERATION OF

EH. KULELN, MD. BLES;

Lecturer on General Anatomy and Physiology in the Medical School of St. Bartholomew’s Hospital, London,

AND

ADAM SEDGWICK, M.A., F.RS., Fellow and Assistant-Lecturer of Trinity College, Cambridge.

VOLUME XXXI.—New Szrizs. Mith Rithographic Plates und Engrabings on Wood,

LONDON:

J & A. CHURCHILL, 11, NEW BURLINGTON STREET. "1890.

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CONTENTS.

CONTENTS OF No. CXXI, N.S., APRIL, 1890.

MEMOIRS :

On Phymosoma varians. By Artuur HE. Surrtey, M.A, Fellow and Lecturer of Christ’s College, Cambridge, and De- monstrator of Comparative Anatomy in the University. (With

- Plates I, II, III, and IV)

The Spinning Apparatus of Geometric Spiders. By Cecit War- BuRTON, B.A., Christ’s College, Cambridge. (With Plate Y) .

On the Structure and Functions of the Cerata or Dorsal Papillee in some Nudibranchiate Mollusca. By W. A. Herpmay, D.Sc., F.L.S., Professor of Natural History in University College, Liverpool. (With Plates VI, VII, VIII, IX, and X) ;

Further Observations on the Histology of Striped Muscle. By C. F. Marswatt, M.B., M.Sc., late Platt Sc Scholar in the Owens College. (With Plate XI)

On Cheetobranchus, a New Genus of Oligochextous eneedatil By Atrrep Grszs Bourne, D.Sc.Lond., F.L.S., C.M.Z.S., Fellow of University College, London, and of the Madras University. (With Plate XII) : :

The Presence of Ranvier’s Constrictions in the Spinal Cord of Vertebrates. By Dr. Wittiam TownsEenD Porter, of St. Louis. (With Plate XII dis)

Prorsssor Birscuu’s Experimental Imitation of Protoplasmic Movement

PAGE

29

41

65

83

91

99

CONTENTS.

CONTENTS OF No. CXXII, N.S., JUNE, 1890.

MEMOIRS :

The Embryology of a Scorpion (Euscorpius italicus). By Matcoitm Lavriz, B.S8c., Falconer Fellow of Edinburgh Uni- versity. (With Plates XIII—XVIII)

On the Morphology of the Compound Eyes of Arthropods. By § Wartasz, Fellow of the Johns Hopkins ones (With Plate XIX) : ;

On the Structure of a Species of Earthworm belonging to the Genus Diacheta. By Franx EH. Bepparp, M.A., Prosector to the Zoological Society of London. (With Plate XX)

Hekaterobranchus Shrubsolii, a New Genus and Species of the Family Spionide. By Fiorence Bucuanay, Student of University College. (With Plates XXI and XXII)

An Attempt to Classify Karthworms. By W. B. Benuam, D.Sc., Assistant to the Jodrell Professor of Sere in a College, London . 2

CONTENTS OF No. CXXIII, N.S., AUGUST, 1890. MEMOIRS:

On the Origin of Vertebrates from Arachnids. By WiL1i1Am Patten,

Ph.D., Professor of Biology in the University of North Dakota, Grand Forks. (With Plates XXIII and XXIV)

On the Origin of Vertebrates from a Crustacean-like Ancestor. By W. H. Gasxewt, M.D.,F.R.S. (With Plates XXV, XXVI, XXVII, and XXVIII)

The Development of the Atrial Chamber of Amphioxus. By E. Ray Lanxester, M.A., LL.D., F.R.S., and AntHUR WILLEY, Student of University College. (With Plates XXIX, XXX, XXXI, and XXXII) : i :

PAGE

105

148

159

175

201

317

379

445

CONTENTS. Vv

CONTENTS OF No. CXXIV, N.S., NOVEMBER, 1890. MEMOIRS: PAGE

On the Structure of a New Genus of Oligocheta (Deodrilus), and on the Presence of Anal Nephridia in Acanthodrilus. By Franx E. Bepparp, M.A., Prosector of the Zoological So- ciety of London. (With Plates XXXIII and XXXIIJa) . 467

Excretory Tubules in Amphioxus lanceolatus. By F. Ernest Weiss, B.Sc., F.L.8., University College, London. a Plates XXXIV and XXXV) : ; 489

Studies in Mammalian Embryology. II.—The evalgoen of the Germinal Layers of Sorex vulgaris. By A.A. W. Huprecut, LL.D., C.M.Z.S., Professor of Zoology in the University of ipeeht (With Plates XXX VI—XLII) : : 499

Terminations of Nerves in the Nuclei of the Epithelial Cells of Tortoise-shell. By Joun Berry Haycrart, M.D., D.Sc. (from the Physiological Laboratory of the Faia o yr (With Plate XLIIT) . ; : . 563

TitTLE, ConTENTS, AND INDEX.

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On Phymosoma varians. By

Arthur E, Shipley, M.A.,

Fellow and Lecturer of Christ’s College, Cambridge, and Demonstrator of Comparative Anatomy in the University.

With Plates I, Il, III, IV.

Tue material which forms the basis of the following paper was collected and preserved by Mr. W. F. R. Weldon, of St. John’s College, Cambridge, during a visit to the Bahamas. On his return to England Mr. Weldon commenced to work at Phymosoma, and made many microscopic sections and drawings. When, however, he received the appointment which he now holds at Plymouth he handed the whole material, together with his drawings, to me, with a request that I would complete the work thus interrupted. This statement will serve to show how much I am indebted to Mr. Weldon, both for material and for many of the drawings ; but I have further to express my indebtedness to him for many suggestions and much help in completing the work he was unfortunately obliged to lay aside.

The observations here recorded were made on a species of Phymosoma (Ph. varians, Selenka) collected in the Bahama Islands.

This species was sufficiently common in the island of New Providence; but it occurred still more abundantly in the lagoon of the Bemini atoll. The specimens were obtained by breaking up soft masses of coral rock with a hammer. Pieces

VOL. XXXI, PART I,—NEW SER. A

2 ARTHUR E. SHIPLEY.

of rock which were completely covered at low water contained many more specimens than those which were left dry by the tide.

The species seems to be capable of much variation; and the descriptions hitherto published are incomplete in one or two important points. A detailed account of the external cha- racters may therefore be not altogether useless.

EXTERNAL CHARACTERS AND EcTopERM.

The length of fully extended specimens averages 50 mm., varying, however, from about 40 mm.to 55 mm. The greatest diameter of the trunk is from 4 mm. to 5 mm.; that of the introvert about 2 mm. The introvert is at least equal in length to the rest of the body.

The head (figs. 1 and 5) bears a crown of about eighteen tentacles, arranged in the form of a horseshoe, with the open ends directed backwards; the whole structure lying far back on the dorsal region of the head (fig. 1). The ends of the teutacular horseshoe are connected with the lower lip; which is a thick vascular crescent enclosing considerably more than three fourths of the circumference of the head (figs. 2 and 6). The mouth is a narrow crescentiform slit, extending between the dorsal margin of the lower lip and the convex surface of the crown of tentacles. These relations of tentacular crown, mouth, and lower lip are shown in the diagram (figs. 1 and 32). It will be seen that in this species the condition of the head presents a marked resemblance to that which obtains in Phoronis.

The tentacles themselves are short and simple, the surface directed towards the outer (convex) side of the lophophor being grooved, and the groove is ciliated; the opposite surface is covered with a deep brown pigmented epithelium (fig. 5).

The space included within the concavity of the lophophor (the representative of the przoral lobe) is covered with a wrinkled, pigmented skin. In its centre lies a deep depression, similar to that of Sipunculus, at the base of which lies the

ON PHYMOSOMA VARIANS, 3

brain; while a sense-pit opens on to it on each side! (figs. 1 and 7).

The introvert is dividable into several regions. Immediately behind the head follows a narrow, perfectly smooth region, extending for about 2 mm. At the posterior edge of this region is attached a small but very extensile collar, its anterior margin being free (figs. 1 and 4.) Behind the attachment of the collar the introvert swells slightly, and there follows a region about 6 mm. in length, which bears about twenty rows of hooks. Then follows a region of variable length, bearing papille; and lastly a second region of hooks, which in our specimens bore from forty to between fifty and sixty rings. Among the hooks of the posterior region are many papille; and these in passing backwards get more and more conspicuous, at the expense of the rings of hooks. These papille also exhibit traces of a tendency to form rings round the base of the proboscis. The characters of the hooks have been well described by Selenka and by Keferstein:? it will be sufficient here to refer to description given by these authors, and to the drawing (fig. 21).

The papille on the introvert have the form shown in fig. 15; they are hemispherical or hemielliptical, being often higher than broad, each having a central opening surrounded by three or four plates of chitin, which often fuse into a single piece; and surrounding this central piece are numerous small rounded plates covering at least the upper half of each papilla.

The papille on the trunk (figs. 11, 14, and 16) have a some- what different appearance, being larger and flatter, and having no marked central plate. They are also surrounded by a much pigmented ring. These trunk papille agree with the de- scription given by Selenka, who, however, seems to have over- looked the difference between the papille in the two regions of the body. The papillz are large and conspicuous at the two extremities of the trunk, where they are present on all sides ;

1 Cf., Speugel, “ Die Sipunculiden,” ‘ Reisen im Archipel der Philippinen,’

Bd. iv, 1883. 2 Selenka, loc. cit., ‘Keferstein, Zeit. fiir Wiss. Zool.,’ Bd. xv, 1865,

4, ARTHUR E. SHIPLEY.

in the middle of the body they are, however, almost entirely confined to the dorsal surface. These papille are shown in fig. 11.

The colour varies in different specimens. The ground colour is always yellowish-brown, with a peculiar iridescence, noticed by other observers: on this are patches of a black or deep brown pigment, which are generally so arranged as to form a few irregular rings in the middle of the introvert and smaller patches on the anterior dorsal part of the trunk. Individuals are, however, found in which the pigment is only very slightly developed; while in others the whole dorsal surface of the body is thickly mottled with dark patches.

The body wall is everywhere covered by an ectodermal epithelium, one cell thick. The characters of the cells pre- senting marked differences in different regions.

The ectoderm covering the lower lip and the outer grooved surface of the tentacles is columnar and covered with short thickly set cilia (figs. 4 and 8).

The preoral lobe, together with the inner surface of the tentacles, is covered by a layer of cubical cells, the outer half of each cell in this region being loaded with granules of a dark brown pigment (figs. 4, 7, and 8). These cells are not ciliated.

The epithelium covering the collar is formed of short cubical cells, which appear to become more flattened when this organ is extended (fig. 4).

On the remainder of the introvert the ectoderm secretes, except in the region of the hooks and papille, a clear homoge- neous cuticle 0:02 mm. thick.

Each hook is secreted by a raised papilla, which projects into the cavity of the hook. The cells covering the papilla being large and cubical, provided with conspicuous spherical nuclei (fig. 21).

Behind each hook is a small organ, apparently sensory, which will be described below.

The ectoderm of the trunk consists of lamellar, dome-shaped cells, secreting a thick cuticle almost ‘04 mm. in thickness (fig. 13). The outer surface of this cuticle is rough and

ON PHYMOSOMA VARIANS. 5

granular; and it absorbs staining fluids with a certain readi- ness, while the main body remains in all the preparations quite unstained. The cuticular substance appears in the greater part of the body to be arranged in wavy columns, running more or less regularly at right angles to the surface of the body, and resting each on a single ectoderm cell (fig. 10). Each column exhibits a further tendency to a laminated structure, the layers composing it lying concentrically to the body of the animal.

A result of the peculiar shape of the ectoderm cells in the trunk-region is the formation beneath them of a series of small cavities, containing a coagulum. By a kind of lifting up of several cells from the adjacent muscles, these cavities commu- nicate with one another and so attain a considerable size (fig. 10). They communicate with the cavities, to be presently described, which lie between the two layers of the papille (fig. 16).

The function of these channels is in all probability con- nected with the circulation of the nutrient fluids; but I have not succeeded in tracing a connection between these and any other of the cavities of the body. The analogy between these spaces and the dermal spaces of Sipunculus need hardly be pointed out. A surface view of the skin shows that the cuticle is broken up into a series of fusiform areas (fig. 11). These areas roughly correspond with the skin-papille, the lines limiting them being formed by thickened portions of cuticle. When the animal is in an expanded condition the areas become thicker and shorter.

The papille of the introvert and trunk are entirely ecto- dermal. Their external appearance has already been de- scribed ; the arrangement seen in section is shown in figs. 14 and 16.

The cuticle seems, in the region round the base of each papilla, to contain irregular spaces, as if its inner and outer surfaces had been pulled apart, an appearance which may, of course, be due to the action of the knife used in cutting sec- tions. On the papilla itself, the plates seen in surface views

6 ARTHUR E. SHIPLEY.

are visible as local thickenings of the cuticle, and are often loaded with a bright yellow-brown pigment.

The body of the papilla has the form of a double cup, as if it had been formed by the invagination of a spherical out- growth of the general ectoderm. The outer layer of the cup is composed of flattened cells, which are continuous with those of the general ectoderm at the base of the papilla, and with those of the inner cup at its apex. The inner layer of the cup consists of large cells, loaded with granules of a bright yellow substance, so that the remains of their protoplasm are seen as slender strings of stained material, separating masses of the yellow formed material. This inner cup contains a small cavity, which communicates with the exterior by the pore at the apex of the papille. Between the two cups is a cavity, continuous with the subepidermal system of spaces above mentioned.

In the absence of a detailed knowledge of the habits of the living Phymosoma it would be rash to assign any function to these very curious organs, but it seems not improbable that the secretion they produce may assist in softening the coral rock in which the animals form long tubular passages.

GENERAL ANATOMY.

The arrangement of the internal organs is shown in fig. 3 which represents a Phymosoma cut open longitudinally and the body wall turned back to expose the viscera. The intro- vert is invaginated to almost its full extent, the true anterior end of the body being at the point where the sense-pits lie.

The longitudinal and circular muscles of the skin have been omitted for the sake of clearness ; a detailed description of them is given below.

The retractors of the introvert are four in number. They fuse round the first half of the csophagus forming a muscular tube, and then separate into a dorsal and a ventral pair. The former are much the shorter pair; between them lies the dorsal blood-vessel, whilst the ventral pair have at their base the generative ridge and between them the nerve-cord. The

ON PHYMOSOMA VARIANS. 7

spindle muscle supporting the alimentary canal is shown running up the axis of the intestinal coil. The cesophagus is anteriorly surrounded by the retractor muscles, but the poste- rior half is free and ends in the coiled intestine. The number of coils varies, usually there are about fifteen. The intestine forms a thicker tube than the cesophagus, it ends in the rectum which passes straight to the anus in the dorsal middle line.

The only part of the vascular system visible is the crumpled dorsal vessel.

The brain is indicated through the walls of the introvert, and close behind it, at the sides, two black spots, the sense- pits, are visible ; the ventral nerve-cord is seen running down the body.

The nephridia or brown tubes are conspicuous objects, vary- ing very much in size and shape in different individuals. Their external opening is at the anterior end and a little in front of the level of the anus. The opening is followed by a short neck which opens into the swollen portion or bladder which passes into the true secreting portion. The anterior half of the nephridia is attached to the body wall by muscle- fibres, the posterior is free (fig. 18).

The generative ridge runs across the body at the base of the ventral retractors (fig. 22). It is sometimes V-shaped, the ridges slanting backward in the middle ventral line.

Tue Muscurtar System,

The muscular system is composed throughout of fusiform fibres with simple pointed ends. Lach fibre consists of an outer contractile and an inner granular portion, the outer por- tion being longitudinally striated. The elongated oval nucleus lies entirely within the inner layer, the nucleus and the con- tractile layer being easily stained, while the inner substance does not absorb staining fluids (figs. 13 and 21).

The fibres of the retractor muscles are much larger than those of the body wall, their diameter being at least twice as great.

8 ARTHUR E. SHIPLEY.

The fibres of the general body wall are arranged in an external circular and an internal longitudinal layer, separated by an exceedingly delicate layer of oblique fibres. This latter can only be seen in surface views, as, owing to its extreme thinness, it is difficult to detect in sections.

The circular muscles commence behind the collar fold, where they form a series of rings round the introvert, one lying beneath each ring of hooks (fig. 1). Posteriorly to the hook-bearing region the circular fibres form a continuous sheath, which extends to the posterior end of the animal (fig. 22).

The longitudinal fibres form a complete sheath round the introvert, commencing anteriorly just behind the attach- ment of the collar. At the posterior extremity of the intro- vert these fibres separate into longitudinal bundles, generally about twenty-two in number, which run parallel with one another down the trunk. In passing backward these bundles gradually fuse with one another, and so become fewer and larger, till near the “tail” they form a series of projecting ridges, giving to a section of the body-cavity in this region a characteristic star-shaped appearance (fig. 18). At the poste- rior extremity of the body the bundles finally unite. The lon- gitudinal bands occasionally give off side branches, which pass into the adjacent bands (fig. 22).

The retractor muscles of the proboscis arise by a common origin from a kind of dissepiment, stretching across the body at the level of the origin of the mantle fold, and just behind the skeletal tissue of the collar (fig. 9). Almost immediately after their origin they split into two bands, which pass backwards, one on each side of the ceesophagus, for about half its length. Each lateral band then again divides into two branches, a shorter dorsal and a longer ventral branch, which run to the body wall, where they fuse with the adjacent bands of longitu- dinal fibres. The ventral bands, being longer than the dorsal, are attached to the body wall behind these, lying one on each side of the nerve-cord, and being connected by the generative ridge. The posterior ends of the retractor muscles are fan-

ON PHYMOSOMA VARIANS. 9

shaped and split up into bundles of fibres, which pass into the adjacent longitudinal bundles.

A special muscle accompanies the nervous system on each side (fig. 29), and is described in connection with the nerve- cord. Its purpose is probably to regulate the movements of this important organ during the eversion or retraction of the introvert.

The spindle-muscle and the intrinsic muscles of the ali- mentary canal are described with the digestive organs, and the intrinsic muscles of nephridia with the account of these organs.

Except along the generative ridge, the body wall is lined by a layer of flat epithelial cells, which is never ciliated, in this respect differing from that of Sipunculus.

THe SKELETAL TISSUE.

A curious form of tissue is found in the collar and the ten- tacular crown of Phymosoma. As it seems to subserve the purpose of supporting and stiffening the collar and tentacles, and as a support for the insertion of the retractor muscles, I propose to call it the skeletal tissue.

The cells composing this tissue are large rounded cells, which lie close to one another, but are not so crowded as to become hexagonal. ‘The cell nucleus is large, and both it and the proto- plasm of the cell staindeeply. Running across the cell, usually in a radial direction, are a small number of wavy lines.

This tissue forms a ring lying in the substance of the collar, which it seems to stiffen. The horseshoe-shaped blood-space lies internal to this tissue, which is thicker at some parts, and thus serves to break up the blood-space as indicated in figs. 4 and 6. It also sends extensions into the tentacles, a group of these skeletal cells heing formed on both sides of the tentacular nerve in each section of the tentacle (fig. 17).

From the position of this skeletal ring in the collar it will be readily understood that it is just in front of the invaginable introvert, and consequently it affords a valuable hold for the

10 ARTHUR E. SHIPLEY.

insertion of the retractor muscles which are attached to this part of the body.

THe ALIMENTARY CANAL.

The digestive tube may be divided into three parts: (1) the cesophagus, which extends from the mouth to the beginning of the coiled intestine; (2) the intestine which forms a close, fairly regular coil with from ten to sixteen turns ; in its coiled state it is almost 10 mm. long; (3) the rectum, which is a straight tube passing from the anterior end of the coil to the anus.

In spirit specimens the whole of the alimentary canal is white in colour, and is usually full of fine sand. A spindle- muscle serves to support and keep in position the coiled intestine and rectum. This muscle arises from the extreme posterior end of the body wall, and passes forward along the axis of the coiled intestine and then parallel with the rectum, to be inserted into the body wall a little in front of the anus (fig. 8). It gives off during its course numerous fibres, which are inserted into the walls of the intestine and rectum. In addition to the spindle-muscle the intestine is held in position by a thin muscle, which arises from the ventral surface of the body and is inserted into the anterior end of the coil.

The position of the mouth has been described above. It is a crescentiform slit, lying between the lip and the convex side of the tentacular crown (fig. 6). It is lined with a continua- tion of the columnar ciliated cells which cover the inside of the lip and the ciliated grooves of the tentacles. The walls of the cesophagus are produced inwards into a series of from six to eight ridges, which reduce the lumen of the esophagus to a star-shaped tube. The grooves between these ridges are continuous with the grooves on the outside of the tentacles (fig. 9). The whole is beset with short thick-set cilia. Surrounding the cesophagus are a few muscle-fibres arranged circularly. For about half its length this first part of the alimentary canal lies between the retractor muscles, which in this region of the body have been reduced to two bundles of

ON PHYMOSOMA VARIANS. 11

fibres by the fusion of the anterior and posterior muscles of the left and right side respectively. These lateral bundles have fused with the cesophagus, a small amount of gelatinous connective-tissue containing branched cells being found be- tween them and the circular muscles of the esophagus. The dorsal blood-vessel lies between the lateral muscles in a groove, closely applied to the dorsal side of the cesophagus, and extending back almost to the beginning of the intestinal coil.

Owing to the presence of very fine sand in the intestine and the delicacy of the tube which made it impossible to satis- factorily wash the sand out, I had considerable difficulty in studying the histology of this part. The intestine is lined throughout by a layer of columnar epithelial cells, one cell thick. The nuclei of these cells are situated near the base. Outside this layer is a thin membrane in which muscle-fibres are sparsely scattered. I do not think the intestine is uni- formly ciliated, but patches of cilia occur here and there. The arrangement of these ciliated patches I failed to make out. There is no groove with long cilia running the whole length of the animal, such as has been described by Keferstein in Sipunculus.

The lumen of the rectum is almost occluded by the presence of numerous folds projecting into it. These folds are covered with a number of columnar cells some of which are ciliated, but the majority are crowded with large vacuoles containing minute granules; these are devoid of cilia. The rectum has no czeca opening into it, such as are found in Sipunculus.

The external cuticle is folded into the anus for a little way, and the circular muscle-fibres of the body wall are thickened around the anus in this region, forming avery efficient sphincter. A number of radially arranged fibres also pass out all round the anus; these fibres are derived from the longi- tudinal muscles. Their action is obviously antagonistic to that of the sphincter.

12 ARTHUR E. SHIPLEY.

THe VASCULAR SYSTEM.

There are two varieties of blood-corpuscle found in Phy mo- soma. The larger kind exist in great numbers in the body- cavity, together with the ripe generative products (fig. 30). They are oval, about 02 mm. long and two thirds as broad ; their protoplasm is very clear and transparent, but the nucleus stains well and they have a very definite outline. The ccelomic fluid, in which these corpuscles float, bathes all the internal organs of the animal, and when the contraction of the poste- rior circular muscles forces the fluid forward it would serve to evert the introvert, which is withdrawn again by the retractor muscles.

The second variety of blood-corpuscle is much smaller than the first, being about half as long and as broad; the proto- plasm is not so transparent and stains more readily. These corpuscles are contained in a close space which is usually called the vascular system. This space may best be described as consisting of three parts, all communicating with one another. The first of these is a horse-shoe shaped space (figs. 2 and 7) at the base of the tentacles. From this space there runs up into each tentacle a series of three vessels which anastomose freely with each other and communicate at the tip. Asa rule sections of the tentacles show one vessel near the inner pig- mented surface of the tentacle, just external to the tentacular nerve and two near the outer surface, one each side of the ciliated groove (fig. 17). The free ends of this horseshoe- shaped space at the base of the tentacles, near the dorsal middle line, are continuous with the ends of another horseshoe- shaped space which lies in the collar. This forms the second of the above-mentioned spaces. As the diagram (fig. 2) shows, it is very irregular in form, breaking up and anastomosing into a number of spaces. This communicates only with the inner smaller horseshoe, between the two is the crescentiform space in which the mouth opens. The third space—usually termed the dorsal blood-vessel—is a very extensile sac running along the dorsal middle line of the esophagus between the

ON PHYMOSOMA VARIANS. 13

right and left retractor muscles (figs. 2, 3, and 9). It usually extends about 3 cm. behind the head, and it ends blindly behind. Anteriorly it opens in the middle ventral line into the smaller or tentacular horseshoe, and at the point of junction is a large sinus which surrounds about three quarters of the brain—in fact, all those parts which are not in contact with the epidermis (figs. 2,4, and 8). The nervous matter is thus in close contact with the blood, being separated only by a thin layer of con- nective tissue, and the endothelium of the blood-space (fig. 27).

The walls of this third part or dorsal vessel are muscular, and in some specimens are much contracted and crumpled. This vessel appears to serve as a reservoir for the corpusculated fluid, and when it contracts and the fluid is forced forward, it would serve to evert the lip and extend the tentacles. The whole of this space is lined by flat epithelium. I have never seen cilia on the walls, and it is entirely closed.

Tue NEFHRIDIA.

The nephridia or the renal organs are in the form of a single pair of ‘‘ brown tubes,” as in other Sipunculide. They lie on either side of the middle ventral line at some little dis- tance from the nerve-cord. Their anterior extremities, near which are the external openings, being a little anterior to the level of the anus (fig. 3).

Each nephridium is about 1 cm. long, the length in preserved specimens varying according to the space of contraction of its muscular coat; by means of this muscular layer the whole organ has the power of shortening and dilating, and also of throwing itself into a number of curious curves.

At the anterior extremity is a dilated bladder, the diameter of which is from four to five times that of the posterior cellular portion of the organ. The internal opening is situated at the anterior extremity of the bladder and is provided dorsally with a prominent ciliated lip! (fig. 18). The external orifice is just

1 The existence of this opening is doubted by Selenka, ‘ Die Sipunculiden,’

but it is sufficiently obvious in all the specimens. It was demonstrated in another species of Phymosoma by Dr. Spengel.

14, ARTHUR E. SHIPLEY.

behind the internal, and opens also into the bladder. The opening to the exterior is surrounded by a thickened ring of connective tissue with muscle-fibres intermingling, the latter forming a sphincter. The walls of the passage are folded and lined with cubical epithelial cells. The communication between the internal opening and the bladder is effected by means of a short passage, the epithelium of which is ciliated. The walls of the bladder itself are formed of a single layer of cubical cells, a middle coat of irregularly arranged muscle-fibres, and an external investment of peritoneum. The relations of the bladder and its openings will be evident from the diagram, fig. 18. The walls of the bladder are very elastic, they contain many muscular fibres, and are lined with cubical epithelial cells.

The tubular portion of the kidney is a backward prolonga- tion of the bladder, and is attached from the anterior half of its course to the body wall by a mesentery, its posterior half being free. The tube possesses anteriorly a simple lumen, which is broken up posteriorly by a number of septa, producing an appearance which reminds one of that presented by the interior of a frog’s lung, the transition between the two regions is very gradual.

The epithelium lining the tubular portion of the kidney is generally one cell thick; it is produced internally into a series of long papille, which are separated from one another by a series of depressions (see figs. 19 and 20).

The cells forming the papille are extremely long, and are loaded with fine, yellowish granules. In specimens killed during the functional activity of the organ these papilla-cells are furnished at their inner extremities with a series of large thin-walled vesicles, which appear to be thrown off from time to time into the lumen of the kidney (fig. 20).

The granules, with which the kidney-cells are loaded, appear to decrease in number as the vesicles are approached ; and it seems possible that the excretory products of the nephridial cells are stored up in the vesicles before being thrown, together with the vesicles themselves, into the nephridial tube. The

ON PHYMOSOMA VARIANS. 15

whole process is very similar to what takes place in a mammary gland during the excretion of milk. Théel mentions that the excretory organs of Phascolion emitted yellow vesicles which resembled drops of oil when the living animal was disturbed.!

Between the papille lie a series of hemispherical depressions lined by a flattened epithelium, the cells of which are usually loaded at their base with the yellow granules above men- tioned. ‘These cells seem to develop into the high columnar cells described above.

The muscle-fibres form an irregular network outside the nephridial cells, lying chiefly at the bases of the papillae. The hemispherical depressions seem to pass through the meshes of the muscular coat, and to lie in direct contact with the perito- neal investment of the organ (figs. 19 and 20), forming a series of projections visible on the external surface.

The peritoneal epithelium which surrounds the kidney is dis- tinguishable from the nephridial cells by the greater ease with which it absorbs staining fluids, and by the absence of secretion granules. In the region of the hemispherical depressions the peritoneal cells frequently form thick masses several cells deep.

It is difficult to avoid the conclusion that the excretion pro- ducts are passed through the peritoneal cells to the cells of the hemispherical cups, and thence to the cells of the papille, the internal opening of the nephridium having relation chiefly to its function as a generative duct.

The relative amount of the secreting epithelium to the cubical epithelium lining the bladder varies greatly ; in one specimen even the area between the external opening and inner end of the internal opening was lined with the former cells, thus reducing the bladder to a very small structure.

The lumen of the nephridium contains nothing but the vesicles above described, together with ripe ova or spermatozoa. It is remarkable that the cwlomic corpuscles appear never to pass through the internal opening of the organ.

1 Théel, “Recherches sur le Phascolion strombi,” ‘ Kongl. Svenska Ve- tenskaps-Akademiens Handlingar,’ Bandet 14, No. 2.

16 ARTHUR E. SHIPLEY.

Tue Nervous System AND SENSE-ORGANS.

The brain is a bilobed organ, continuous by its anterior face with the ectoderm of the invaginated preoral lobe, and surrounded elsewhere by a process of the lophophoral blood- vessel, from which it is separated, not only by the endothelium of the vessel, but also by a connective-tissue capsule (see figs. 2,4, 8, and 27). The groove between the two lobes is deepest and widest on the anterior surface, where the substance of the brain is continuous with that of the przoral ectoderm.

In the brain, as in the ventral nerve-cord, the ganglion-cells are aggregated in the side nearest the skin; they are on the dorsal side of the animal in the brain, on the ventral in the nervous system.

As the figs. 24, 25, and 26 show, there is a cap of ganglion- cells covering the anterior, dorsal, and posterior surfaces of the brain. The ventral surface is not invaded by the ganglion- cells; but here the fibrous tissue, which makes up the rest of the brain, comes in contact with the thin connective capsule. It is this region of the brain which projects into the blood- sinus.

The majority of the ganglion-cells are small, with deeply stained nuclei, occupying about one half of the cell; they are either unipolar or bipolar. At the postero-dorsal angle of the brain, however, a certain number of giant ganglion-cells are found (fig. 27). These cells have a diameter of 02 mm., at least four times that of the smaller cells; their nuclei are rela- tively smaller, and they are unipolar. I was unable to trace what becomes of the fibres given off from these giant-cells. No such giant-cells occur in any other part of the nervous system.

A pair of sense-organs, usually described as eyes, lie em- bedded in the substance of the brain.

Each of these sense-organs has the form of a long tube bent upon itself, so that one limb is nearly at right angles to the other. The outer limb, the lumen of which is narrow, opens on to the surface of the przoral lobe (figs. 1 and 25), the opening lies

ON PHYMOSOMA VARIANS. 1;

at the dorsal lateral angle of the brain, just dorsal to where the circumcesophageal nerve-commissure leaves the brain ; the lumen of the inner limb dilates into a vesicular swelling in the substance of the brain (fig. 23); the whole tube has, therefore, nearly the shape of a retort, and lies entirely in the lateral part of the brain. The wall of the tube is everywhere formed by a layer of clear, nucleated cells. In the outer limb these cells form a fairly regular columnar epithelium one cell thick, which becomes less regular as the inner limb is approached. The cells bounding the inner limb are arranged irregularly, and they appear to send out processes from their peripheral extremi- ties, which may be supposed to communicate with the pro- cesses of adjacent nerve-cells. The cells of the inner limb also secrete a deep black pigment, which lies in that portion of each cell which is turned towards the lumen of the tube. A clear coagulum sometimes lies in the cavity of this sense-pit. These organs are visible as two black spots at the level of the brain in the dissected animal (fig. 3).

No trace exists in this genus of the curious finger-like pro- cesses which project from the brain of Sipunculus into the body-cavity.

Three pairs of nerves are given off from the brain: (1) dorsally, a small pair supplying the skin of the preoral lobe— these lie nearest to the middle line (fig. 26) ; (2) ventrally, a nerve on each side, going to the corresponding area of the lophophor, and supplying a branch to each tentacle (fig. 24) ; (3) and posteriorly on each side arises a nerve which passes round the cesophagus, and joins its fellow of the opposite side to form the ventral cord (fig. 24). The lophophoral nerve arises between the point of origin of the nerve of the preoral lobe and the exit of the circumcesophageal commis- sures.

The ventral cord itself shows no trace either of a division into two halves, or of a segregation of its nerve-cells into ganglia, It runs along the ventral surface of the body as a perfectly uniform filament, terminating posteriorly without any ganglionic swelling such as that found in Sipunculus.

VOL. XXXI, PART I.——NEW SER. B

18 ARTHUR E. SHIPLEY.

The fibres are on the dorsal, the cells on the ventral side of the cord.

Along each side of the nerve-cord runs a longitudinal band of muscle-fibres, the cord and its pair of muscles being together enclosed in a special peritoneal sheath. The space between the sheath and the cord is filled with a peculiar connective tissue (fig. 29), which has been regarded by some observers as clotted blood, the cord being said to lie in a blood-vessel. My preparations afford no evidence in support of this view; and I am strongly of opinion that the substance lying