ges ni der ss ite! athte eRe ’ beh SLE AT Ble ay 4A amu anal abe ere int nen ¢ aire rerte ome ; Hie ue fe air is ine i a it et ¢ ite om prvewaeeGA Seer na ae eee ee es Pe etait ret Fiplertre tPirbeltat trot) star ip torbstaraverteereny! eRe Hf pt pipesitrauestt Sacpiats oletb-s tae ies SAR or iy gl aie © =TBEEs iat eet TTY TREN LE RTE LSS whe Bs tet eehets ts? an eet Stree fie aate tote ats foatil tg 4 Seeeosiyeay ice wach ahek hae CORNELL UNIVERSITY. THE Rosmell P. Flomer Library THE GIFT OF ROSWELL P. FLOWER FOR THE USE OF THE N. Y. STATE VETERINARY COLLEGE. 1897 Cornell University Libra Amphioxus and the ancestry of the verteb DATE DUE pS a a GAYLORD Columbia Gnibersity Biological Series. EDITED BY HENRY FAIRFIELD OSBORN. - FROM THE GREEKS TO DARWIN. By Henry Fairfield Osborn, Sc.D. Princeton. . AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES. By Arthur Willey, B.Sc. Lond. Univ. . FISHES, LIVING AND FOSSIL. An Introductory Study. By Bashford Dean, Ph.D. Columbia. . THE CELL IN DEVELOPMENT AND INHERITANCE. By Edmund B. Wilson, Ph.D. J.H.U. Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924001026131 a2dn dst Oty ‘(VNISSTPT) OV LV ONVAINVG ELL NI SAXOINdIWY COLUMBIA UNIVERSITY BIOLOGICAL SERIES. TI. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES BY ARTHUR WILLEY, B.Sc. Tutor 1n Brotocy, CoLtumBiA CoLLEGE; BALFouR STUDENT OF THE UnIvEeRSITY OF CAMBRIDGE WITH A PREFACE Sf, f : Se veh SY HENRY FAIRFIELD OSBORN New Pork MACMILLAN AND CO. AND LONDON 1894 All rights reserved I \ 1 TJTLA Yo 'O CopyRIGHT, 1894, By MACMILLAN AND CO. Norwood press. J. S. Cushing & Co. — Berwick & Smith. Boston, Mass., U.S.A. Dedicated IN GRATITUDE AND ESTEEM TO PROFESSOR E. RAY LANKESTER, F.R.S. BY HIS FORMER PUPIL THE AUTHOR PREFACE, Tuis volume originated in a course of University lec- tures prepared at my suggestion by the author. It seemed important that he should bring within the reach of students and of specialists among other groups, his own extensive observations upon Amphioxus and other remote ancestors of the Vertebrates, as well as the general litera- ture upon this group. While our detailed knowledge of the structure and habits of these animals has been rapidly increasing in recent years, it is still in the main very widely scattered in monographs and special papers. Probably no single group illustrates more beautifully the principles of transformism ; for the Protochordates in their embryonic development exhibit remarkable reminis- cences of past adaptations, and, in their adult develop- ment, the most varied present adaptations to pelagic, deep-sea, littoral, free-swimming, and sessile life. As Lankester has shown, the Ascidians alone give us a whole chapter in Darwinism. But degeneration and change of function constitute only one side of their history. In vii vill PREFACE. progressive development some of these types have come to so closely resemble, superficially, certain of the larger groups of Invertebrates, such as the Molluscs and Worms, that it is only at a comparatively recent date they have found their way out of these groups into the Protochor- data. Many of these misleading resemblances are now interpreted as parallels of structure springing from parallels in life habit, seen not only in the general body form, but in special organs, such as the breathing apparatus of the Ascidians and Molluscs. By the side of parallelisms are real invertebrate and vertebrate affinities; so that the problem of resolving these various cases of original and acquired likeness in their bearing upon descent has. become one of the most fascinating which modern Zodlogy affords. For example, among the real invertebrate ties of the Protochordates are the ciliated embryos of Balanoglossus and Amphioxus, the Tornaria larva and ciliated ectoderm of Balanoglossus. The nervous system of Balanoglossus presents both ver- tebrate and invertebrate characters ; the respiratory sys- tem is identical with that of Amphioxus, while in the embryonic development there are many resemblances ater se. In short, in Balanoglossus and the Ascidians the invertebrate type of structure, whether original or ac- quired, predominates. But in Amphioxus the balance is far on the other or vertebrate side of the scale, and this, with its resemblances to lower forms, gives us the con- PREFACE. 1x necting link between Protochordate and Chordate organ- isation. Before entering into any of these discussions, the author has given a thorough systematic and structural treatment, especially of Amphioxus. This exquisite form, Amphioxus, is of almost world-wide distribution and has enjoyed the attention of every great zoologist for over half a century, yet the most recent studies upon it have been among the most productive of discovery. Its interest and value as an object of biologi- cal education has steadily increased with the knowledge that in contrast with all the related forms, it stands as a persistent specialised but not degenerate type, perhaps not far from the true ancestral line of the Vertebrates. ‘ H.F. O. CONTENTS. S55 PAGE INTRODUCTION: y extended. mm. Mouth. me. and Ze. Right the body, or, in other words, and left enteroccelic cavities. s¢, Stomach. at the apex of the preoral “ ree lobe, in Tornaria, there is an ectodermic thickening in which nerve-cells and nerve-fibres and a pair of simple eyes have become differentiated. This is the so-called apical plate, and it constitutes the central nervous system of the larva. It can be recognised for some time after the metamorphosis at the tip of the proboscis, but eventually disappears completely. A similar apical plate occurs in 256 THE PROTOCHORDATA. a great number of Invertebrate larve, and is especially characteristic of the free-swimming larve (Trochophores, or Trochospheres) of Annelids and Molluscs. We shall return to this later. In Tornaria a single contractile cord passes from the apical plate to the anterior enteroccel. There is no apical plate in Auricularia, nor in most of the other Echinoderm larve; but there is reason to sup- pose that it has been secondarily lost, since a transitory ectodermal thickening at the apical pole can frequently be observed in the course of their development ; and, moreover, in what is probably the most primitive Echino- derm larva known (viz. the larva of the Crinoid, Azztedoz), there is a well-developed apical plate. Metamorphosis of Tornaria. The metamorphosis of Tornaria, as originally described by Alexander Agassiz, takes place with relative sudden- ness. According to the more recent account of the meta- morphosis given by Morcan, a marked diminution in size occurs; the internal organs are drawn together in such a way that the larval cesophagus, with the gill-pouches (see Fig. 120), is drawn backwards into the body, and the anterior enteroccel, as already described, is carried for- wards into the preoral lobe. The longitudinal (circum- oral) ciliated band, which was the first to develop, is also the first to disappear, while the posterior circular band persists to a somewhat later stage. The Nemertines. It is thus evident that Balanoglossus, especially through its Tornaria larva, shows undoubted marks of affinity to gt uaa) nee extemal ser- similar hakbiese Or muc OI tae UmiCeuuisar iMresu 258 THE PROTOCHORDATA. place from the tip backwards by the in-rolling of its walls. According to the graphic description of HuBRECHT, it is retracted ‘in the same way as the tip of a glove finger would be if it were pulled backwards by a thread situated in the axis and attached to the tip.” When at rest within the body the proboscis lies freely within a hollow cylinder, the wall of which is thick and muscular, and constitutes the prodoscis-sheath (Fig. 123). Fig. 123.— Diagrammatic transverse section through the middle of the body of a Nemertine. (After LANG, Text-b00k of Comp. Anat.) é.m, Basement-membrane. c¢.m. Circular muscles. d@.. Dorsal or “ medullary" nerve. d@.v. Dorsal blood-vessel. g. Gonads. inf. Intestine. 27. Longitudinal muscles. /.7, Lateral nerves. /.v, Lateral blood-vessel. ~. Proboscis. 2.5. Pro- boscis-sheath. Sometimes beneath the ectodermal epithelium of the Nemertine proboscis there is a continuous sheath of nerve- fibres, comparable to the nervous plexus in the proboscis of Balanoglossus. Partly, therefore, on account of its structure, and partly on account of its topographical relations when extruded, we are led to suppose that a certain homology exists NEMERTINES. 259 between the retractile proboscis of the Nemertines and the non-retractile proboscis of Balanoglossus (BaTESoN). In the most primitive Nemertines the nervous system consists essentially of a somewhat complicated pair of cerebral ganglia and a diffuse nerve-plexus, with nerve- cords lying at the base of the ectoderm.* As the cerebral ganglia probably belong to the same category as the cere- bral ganglia of all other typical Invertebrates, and are not represented in Balanoglossus, we can afford to neglect them at present. Confining our attention to the ecto- dermal nerve-plexus, we find occurring in it, along definite lines, local thickenings, after the same principle, but not all on the same lines, as was described above for Balano- glossus. Directly comparable with the dorsal longitudinal nerve-cord of Balanoglossus, there is a similar thickening or concentration of the integumentary nerve-plexus in some of the Nemiertines, in the dorsal middle line (Car- tnina, Cephalothrix). Hubrecht, who discovered this, calls it the medullary nerve. There is, however, no correspond- ing ventral nerve-cord in the Nemertines, but, instead of this, there is a pair of lateral thickenings, constituting the well-known J/ateral nerves of the Nemertines (Fig. 124). It is usually supposed that the lateral nerves of the Nemertines are homologous with the two halves of the ven- tral nerve-cord in the Annelids. In the Annelids the primitive lateral nerves (which are so typical of the Platy- helminths, or flat-worms) have approached one another in the mid-ventral line, and have often undergone intimate fusion together. In some cases, however, they are separated from one another by a wide interval (Sabellaria, etc.). * HUBRECHT compared the lobes of the cerebral ganglia of a Nemertine to the cranial ganglia of the Vertebrates, the lateral nerves to the Rami laterales vagi, and the proboscis-sheath to the notochord. 260 THE PROTOCHORDATA. In the Annelids, in contrast to the Nemertines, the gan- glion-cells are not distributed uniformly along the whole length of the nerve-cord, but are collected together to form definite ganglionic swellings. It is, therefore, very significant that in the Nemertines we have a median dorsal “medullary” nerve, in addition to the elements which constitute the ventral nerve-cord of the Annelids. In many Nemertines the dorsal and lateral nerve-cords do not continue to lie in the ectoderm throughout life, but Ma id Ls ee AD gE Fig. 124.— Diagrammatic view of anterior portion of a Nemertine, from the left side. (After HUBRECHT, from LANG.) a./, Anterior lobe of brain. #./. Posterior lobe of brain. 2. Opening of pro- boscis. mm. Mouth. d.2. Dorsal nerve. /, Lateral nerve. 4.2, Ring-nerves. sink deeper into the body, and so come to be separated from the ectoderm, first by the basement membrane, and then by one or more muscular layers of the body-wall. In the Hoplonemertea (those in which the proboscis is armed with stylets) the medullary nerve is absent. In all cases, however, the longitudinal nerve-cords remain connected with one another by a more or less plexiform arrangement of nerve-fibres ; although sometimes a more definite con- nexion, by means of metameric ring-nerves, has been observed by Husrecnt (Fig. 124). There is no true celom in the Nemertines, and the space between the alimentary canal and body-wall is oc- cupied by a gelatinous mesenchyme, Saguenie nuscul and connective tissue elements. In Balance De OSS ity of the celom becomes largely obliterated in the adult by the proliferation of cells from the epithelium of its walls, thus filling up the cavities with a more or less soli paren vie matous tissue. mentary canal, sete with paired lateral outgrowths or z, and a terminal anus. semblance to those of Balanoglossus. They occur as a metameric series of paired sacs, which alternate with the above-mentionec communicate with t . 1 ~ + fol ae the exterior by at first dad, 238 mm } Jaearre = = ntl >} hol! -ad ry + Balanoglossus, subsequ g hollowed out and } > a lat +) ~ + * Opening above the lateral cords (Fig. Se chanld “ited Gi Finally it should be pointed out organs, in the form of a well-develo elongated eph provided wita *end-sacs, re present in the Nemertines, nothing of tne kind has yet been detected in Balanoglossus. CEPHALODISCUS AND RHABDOPLEURA. It is interesting to note that there are some remarkable animals which stand in a similar relation do to Amphioxus. aqgoes not produce and Azaé- two ¢ 5 Opie 262 THE PROTOCHORDATA. a U-shaped alimentary canal. Both are deep-sea forms, Cephalodiscus having been dredged during the Challenger Expedition, from the Straits of Magellan, at a depth of 245 fathoms ; while Rhabdopleura was first dredged indepen- dently, off the Shetland Islands, at go fathoms, by the Rev. Fig. 125. — Cephalodiscus dodecalophus, from the ventral side. (After M’INTOSH.) Actual length of polypide from extremity of branchial plumes to the tip of the pedicle is about 2 mm. é.s. Buccal shield; the shading on its surface indicates pigment-markings. At the tip of the pedicle, buds are produced. Canon Norman, and off the Lofoten Islands, at 200 fath- oms, by Professor G. O. Sars (1866-68). Rhabdopleura is the name given by ALLMAN (1869), who published a short account of it; and it has since been described by Sars, LANKESTER, and G. H. Fow er. ; The account which we possess of Cephalodiscus forms one of the Challenger Reports, and was written by Pro- fessor W. C. M'Intoss, who made out the main features of its anatomy. It was further treated, from a morpholog- ical standpoint, by Sipney F. Harmer, who pointed out its remarkably close afhnity to Balanoglossus. The most important morphological features in the anat- omy of Cephalodiscus are shown in Figs. 125-127. The individuals live in colonies, in a “house” or which consists of a ramifying and anastomosing system of tubes, the walls of which are composed of a semi-trans- parent, gelatinous material, whose outer surface is covered with spinous projections. The walls of the ccencecium are furthermore perforated by numerous apertures, which allow of the ingress and egress of water. The adult members of a colony have no organic con- nexion between themselves, but each one is independent and free to wander about the tunnels of the ccencecium. Although Cephalodiscus has not been studied in the living condition, there is every reason to suppose that it moves about in its tube by means of the large éuccal shield (Fig. 125) overhanging the mouth, by which it can attach itself to the inner surface of the tube, and then help itself along by the curious pedie/e which occurs ventrally near the hinder end. It thus seems probable that this pedicle can be used as a sucker, but its chief function lies in the production of buds which grow out from it, and eventually become detached. Bateson has described a somewhat similar sucker at the hinder end of the body in voung individuals of Balanoglossus (Fig. 113) Behind and above the buceal shield there is a row of twelve tentacles or branchial plumes. each possessing a central stem or shaft which carries numerous lateral 264 THE PROT OCHORDATA. pinne. An important function of these plumes is to produce currents of water by the action of their cilia, which vibrate in such a direction that the water with food-particles is led into the mouth. The superfluous water is led out from the proximal portion of the aliment- ary canal by a single pair of g7//-s/zts which are not visible in surface view, since they are overhung by a fold of the integument known as the fpost-oral lamella or operculum, corresponding to the posterior free fold of the collar in Balanoglossus (Fig. 126). In its internal organisa- tion, if due allowance be made for its U-shaped ali- mentary canal, Cephalodis- cus greatly resembles Bala- noglossus (Figs. 126, 127). The buccal shield of the the equivalent of the probos- former is obviously Fig. 126. — Longitudinal frontal (right and left) section through an adult Cephalo- discus. (After HARMER.) éc2, Second portion of body-cavity (collar-ccelom). 6c3. Third portion of body-cavity (trunk ccelom). 47. Pharynx. cis of the latter, and the cavity which it contains cp. Collar-pores. gs. Gill-slits. zz. In- corr : testine. 7.5. Nervous system. of. Oper- : espands to the probos culum. oes. Esophagus. st. Stomach. cis-cavity. Moreover, the z, Base of tentacle. : : ‘ proboscis-cavity in Cephalo- discus (z.e. the cavity of the buccal shield) communicates with the exterior by ‘two proboscis-pores placed right and left of the dorsal middle line. Following behind the buccal shield is the col/ar-region, from which the branchial plumes arise dorsally, while CEPHALODISCUS. 265 laterally and ventrally it is produced into a free fold to form the above-mentioned operculum. The collar-region contains a section of the ccelom which is precisely homolo- Fig. 127. — Longitudinal sagittal section through an adult Cephalodiscus. (After HARMER.) The section is supposed to be taken sufficiently to one side of the middle line to allow of the representation of one of the ovaries and one of the proboscis-pores. a. Anus. 6.c. Trunk-cceelom. c.c. Collar-ceelom, ch, Notochord. zn. Intes- tine. m. Mouth. #.s. Nervous system. of. Postoral lamella (operculum). ov. Ovary; the oviduct is deeply pigmented. f.c. Praeoral coelom (cavity of buccal shield), ff. Pharynx. .f. Proboscis-pore. ped. Base of pedicle. st, Stomach. gous with the collar-cavities of Balanoglossus. As in the latter form, it communicates with the exterior by a pair of collar-pores which open at the level of the gill-slits. 266 THE PROTOCHORDATA. The collar-ccelom is continued posteriorly into the opercu- lum, and anteriorly into the twelve tentacular appendages. Finally, behind the collar comes the region of the body containing the viscera, which are surrounded by the third section of the ccelom. Only the female reproductive organs have been observed up to the present time in Cephalodiscus. They occur as a pair of gonadic sacs, opening to the exterior on each side of the dorsal middle Jine between the anus and the central nervous system. The latter is very simple, being represented merely by a dorsal thickening of the ectoderm, with nerve-fibres in the region of the collar and posterior portion of proboscis. Finally, a short notochordal diverticulum projects into the base of the buccal shield as in Balanoglossus. Rhabdopleura differs considerably from Cephalodiscus in many respects, but, nevertheless, has some fundamen- tal characteristics in common with it. In Rhabdopleura the individuals of a colony are not independent, but are connected with each other by a common cord or cau/us, which represents the remains of the contractile stalks of the polyps. As the growth of the colony proceeds, the distal portions of the stalks (7.e. the portions farthest away from the animals) become shrunken and hard. The buds arise from the soft portions of the caulus, and never be- come detached as they do in the case of Cephalodiscus. There is only a single pair of tentacular plumes in Rhab- dopleura. Fow cer has recently shown that in Rhabdopleura the ceelom, whose existence was first established by Lay- KESTER, exhibits the same subdivisions as have been mentioned above for Cephalodiscus; namely, (1) the cavity of the large buccal shield, (2) the collar-cavity opening PRALORAL LOBE. 267 to the exterior by a pair of dorsally placed collar-pores, and (3) the body-cavity proper surrounding the alimentary canal. According to Fowler, who has recently described them in Rhabdopleura, the nervous system and notochord have essentially similar relations to those which obtain in Cephalodiscus, but there are no proboscis-pores and no gill-slits. THE PRAORAL LOBE OF ECHINODERM LARVA. In the previous pages a good deal of stress has been laid on the existence of a przoral lobe in the various types considered. We have recognised it in the snout of Am- phioxus (preeoral ccelom + przeoral pit), in the proboscis of Balanoglossus, the fixing organ of the Ascidian tadpole, and in the buccal shield of Cephalodiscus and Rhabdo- pleura. From a morphological standpoint the przoral lobe is probably one of the most important, as it is certainly one of the oldest, structures of the body of bilateral animals, and it becomes, therefore, a matter of the first moment to be able to trace the modifications which it has undergone along the different lines of evolution which have culmi- nated in the existing types of animal life. The subject is a very large one, and can only be treated here in its broadest outlines. It is now very generally admitted by zodlogists that the Echinoderms (star-fishes, sea-urchins, etc.) owe the radial symmetry, which is one of the most obvious characteristics of their organisation, to their having been derived from bilaterally symmetrical ancestors, which became adapted to a fixed or sessile existence. If this view is correct, and there is good reason for supposing that it is, it follows that the majority of living Echinoderms have secondarily 268 THE PROTOCHORKRDATA. lost their sessile mode of existence, and have again become free-living g, retaining, however, their radial symmetry. At the present time the fixed habit of life is only retained by the members of one of the subdivisions of the Echino- derm class; namely, the Crzzozdca. Most genera of Crinoids (RAtsocrinus, Pentacrinus, etc.) remain fixed by a long, jointed stalk throughout life ; but the well-known “feather-star,”’ Antedon rosacea, is only fixed during a certain period of its larval development. At the close of the period of fixation the body of the animal, or, as it is called, the ca/yx, breaks away from the stalk by which it was attached to the rocks, and so begins to lead a free existence, being capable of swimming vigorously by the flapping of its arms. Although the existing Crinoids have become extensively modified along their particular line of evolution, yet there is reason to believe that they represent the more im- mediate descendants of the primeval form which ex- changed its primitively free life and bilateral symmetry for a sessile existence and radial symmetry. This view is strengthened by the character of the free-swimming larva of Antedon. This larva does not possess, in any extrava- gant degree, those fantastic structures which are so characteristic of other Echinoderm larve, such as the provisional ciliated processes or arms of the “ Pluteus” (larva of sea-urchins), or the undulating ciliated bands of Auricularia. On the contrary, the larva of Antedon is a simple barrel-shaped organism, with regular ciliated bands pass- ing around it (Fig. 128). Perhaps the structure which, above all, stamps the free- swimming larva of Antedon as having, from a phylogenetic point of view, a more primitive type of organisation than PRAEORAL LOBE. 269 that of other Echinoderm larve, is the well-developed apical plate at its anterior extremity. We may express this in other words by saying that the larva of Antedon possesses a central nervous system at the apex of its preoral lobe. That the pre- oral lobe in this larva is not sharply marked off from the rest of the body is a detail of no morphological signifi- cance. The apical nervous sys- tem of the Antedon larva was discovered in 1888 by H. Bury, and has been Fig. 128.—Free-swimming larva of Antedon rosacea, from the ventral side. more clearly brought out (afer serticER.) and emphasised in a recent ap. Apical pole. 6b. Ciliated bands. J. Fixing disc. v. Vestibulum (so-called work by Dr. OSWALD SEELI- ijarval mouth, although at this stage cer, At the point which is “PY 7 otedermie groove). marked externally by the anterior tuft of long cilia in Fig. 129 there is a slight groove in the ectoderm below which nerve-fibres and ganglion-cells can be identified. Seeliger further describes a pair of longitudinal nerves running from the nervous area of the apex along the ventro-lateral margins of the body. As already indicated, the apical plate is, as a general rule, conspicuous by its absence in the typical Echinoderm larva. In the free-swimming larva of Antedon, however, it is emphatically present, although destined to become entirely aborted after the fixation of the larva. In most Invertebrate larve in which an apical plate is present (e.g. the Trochophore-larva of Annelids and Mol- luscs) it becomes, during the metamorphosis, involved in other ectodermic thickenings of the przoral lobe, which 270 THE PROTOCHORDA TA. w ie ook. Be. collectively give rise to the cerebral or supracesophageal ganglion. The apical plate may thus be defined as a primitive central nervous system at the apex of the preoral lobe, being the forerunner and formative centre of the cerebral ganglion of the Invertebrates. Although, with the exception of the Crinoids, there is no apical plate in the typical Echinoderm larva, yet, as noted above, in many cases a curious transitory lengthen- ing of the ectodermic cells at the apical pole has been, and can be without great difficulty, observed in larva of star-fishes and sea-urchins. This alone would seem to indicate the former enist- ence of a central nervous system at the apex of the preoral lobe in the bilateral ancestor of the Echinoderms. he way in which the Fig. 129. — Larva of 4stering viewed as a transparent object from th ss left side. (After LUDWIG.) of the przoral Jobe can be . Enteric cavity. Ze. Left entero- ee a1 3 c ccel, communicating with the right entero- replaced by a dilatation of ccel through ¢./, the preoral lobe. st the enteroccel has been de- Stomodaeum. primary blastoceelic cavity ong scribed above, both for Tor- naria and for the larva of dAsterias vulgaris (Figs. 121-122), In some cases, as in Asteria grébosa, the przoral lobe is occupied by the enteroceel from the very beginning. In the “Pluteus” larva of the Echinids (sea-urchins) the preoral lobe is much reduced; but in other Echinoderms, as in the singular larva of Asterina gtédosa, and in the so-called Brachiolaria-larva of the Asterids (star-fishes) in general, it is very prominent, and serves as an etfective locomoton (creeping) organ. PRAEORAL LOBE. 271 The very interesting observation has recently been made by MacBripg, that the larva of Asterina gibbosa actually undergoes temporary fixation at the beginning of the metamorphosis, the fixation being effected by the preoral lobe in a manner strikingly similar to that of the larvee of Antedon and of Czona. In the larva of Antedon the adhering disc, by which the larva eventually fixes itself to some foreign surface, is placed near the front end of the przeoral lobe immediately below the apical plate. The central nervous sys- tem of the adult Echinoderm arises in entire indepen- dence of the actual or sup- pressed apical nervous sys- ; ee Fig. 130.— Larva of Asterina gibbosa, tem of the larva, and not at viewed as an opaque object from the left all from the ectoderm of the sea scare Lt preeoral lobe. We have thus seen how within the limits of a single group (viz. the Echinoderms) the przoral lobe can become completely emancipated from the central nervous system ; and we have further recognised the fact that whether the cavity of the przoral lobe is a derivative of the primary or secondary body-cavity, whether it contains loose mesen- chyme or is lined by an endothelium, the morphological value of the przeoral lobe itself remains the same. THE PRAORAL LOBE OF THE PROTOCHORDATES. It is probable that the misunderstandings and disagree- ments which are of such frequent occurrence among mor- phologists with regard to the comparison of the types of central nervous system presented respectively by the 272 THE PROTOCHORDATA. Vertebrates and the Invertebrates, are largely due to the failure to detect some general principle of evolution to which that archaic structure, the preoral lobe, has been subjected. Nevertheless, there are many indications which point irresistibly to the conclusion, which I have recently brought forward, that the prime factor which must be recognised in the evolution of the przeoral lobe, from the relations which it presents in the Invertebrates to those which it holds in the Protochordates and Vertebrates, is its emancipation from the central nervous system. In the great groups of the Annelids, Molluscs, and Arthropods, the przoral lobe (prostomium, procephalic lobe) is essentially the seat of the brain or cerebral gan- glion. The latter, through its representative, the apzcal plate, is the main and often the sole element of the central nervous system in the Trochophore-larva of Annelids and Molluscs.* * In speaking of the apical plate as the forerunner or formative centre of the cerebral ganglion, it must not be assumed that these are not distinct structures. The apical plate is essentially median and unpaired, while the cerebral ganglion is paired. They can both, however, be included under the general term, apical nervous system, since they arise from the ectoderm of the preoral lobe. On the other hand, the cerebral ganglion may arise inde- pendently of an apical plate; as, for instance, in Lumdbricus, where there is no apical plate, or in the Memertines, where the apical plate is discarded together with other larval structures (Pilidium). Again, as in Lumbricus and many other cases, the cerebral ganglion, after having separated from the ectoderm of the przeoral lobe, may recede backwards for a considerable dis- tance, so as not to lie in the przeoral lobe in the adult. It is possible that the position of the cerebral ganglia of Nemertines may be accounted for by some such phylogenetic recession from the przeoral lobe. If necessary, it might be said that the praoral lobe can acquire emancipa- tion from the central nervous system by a simple recession of the cerebral ganglion. In the case of the Protochordates, however, on the view here advo- cated, the proeoral lobe has acquired emancipation from the central nervous system, not by the mere recession, but by the complete disappearance of the Invertebrate cerebral ganglion. PREORAL LOBE, 273 At a later stage of development the longitudinal nerve- cord (confining the description to the Annelids for the sake of simplicity) arises tvdependentiy of the cerebral ganglion, from a pair of longitudinal thickenings of the ectoderm near the mid-ventral line, becoming secondarily connected with the cerebral ganglion by the circumaesoph- ageal nerve-collar or commissure As already indicated, it seems probable, as was sug- gested by Batrour and GrGENBAUR, that the ventral nerve-cord of the Annelids is to be regarded as having arisen phylogenetically by the mutual approximation of two such lateral cords as occur in the Nemertines, and like the latter may be supposed to have originated by a concentration on the ventral side of the body of that primitively continuous sub-epidermic nerve-plexus which is such a characteristic feature of the Nemertines. From a consideration of the adult nervous system in the Echinoderms, Nemertines, Enteropneusta (Balanoglossus), Annelids, and Molluses, it is evident that such a con- centration of nervous tissue has from first to last occurred along very different lines. Speaking in broad terms, it may be said that the only portion of the Invertebrate nervous system which, in its prime essence, is invariable and universal (due allowance being made for exceptional cases) is the cerebral ganglion or its forerunner, the apical plate, the seat of which Hes in the preeoral lobe.? Under these circumstances it will suffice to confine our attention to the praesoral lobe, in the belief that if an understanding can be arrived at with regard to that impor- tant structure, one of the chief difficulties in the way of a just conception of the relations existing between Verte- brates and Invertebrates will have been overcome. 274 THE PROTOCHORDATA. Returning now to Balanoglossus, we have to remark that in the Tornaria larva the central nervous system is represented entirely by the apical plate of the przoral lobe, the situation of the apical plate corresponding to the anterior tip of the proboscis of the adult. Unlike the Annelids, however, the apical plate of Tornaria does not become replaced after the manner of the Invertebrates by the development of a cerebral ganglion arising like it from the ectoderm of the przeoral lobe and with it as a formative centre. On the contrary, it completely disappears after the metamorphosis, having become replaced physiologically by the development of the medullary tube in true Verte- brate fashion from the dorsal ectoderm of the collar-region behind the przeoral lobe.* In the Ascidian larva, however, and in Amphioxus, the characteristic Invertebrate apical nervous system no longer appears in any stage of development, its physiological func- tion having been once for all assumed by the medullary tube (cerebral vesicle + spinal cord) which lies par excel- lence behind the przeoral lobe (Fig. 131). Antertor and Posterior Neurenteric Canals, and the Position of the Mouth in the Protochordates. After the postoral medullary tube had led indirectly to the complete obliteration of the preoral apical nervous system, and had attained to such a degree of development as we find, for instance, in the Ascidian tadpole, the central canal of the cerebro-spinal nervous system appears to have acquired remarkable relations with the alimentary canal. At both ends of the body connecting ducts be- * For a detailed account of the formation of the medullary tube in the col- lar-region of Balanoglossus see MoRGAN (Bibliography, Nos. 124 and 125). PR.EORAL LOBE. 275 came established between the nervous and digestive systems, known respectively as the evferior and posterior neurenteric canals. The posterior neurenteric canal is only of transitory occurrence in all existing Vertebrates, and leads from the pe ch Fig. 131. — Diagrammatic representations of the anterior region of the body in (4) an Ascidian larva, (8) larva of Amphioxus, and (C) Balanoglossus. (After WILLEY,) The figure of Balanoglossus was compiled from Bateson’s figures; the pro- boscis-pore is indicated rather too far forwards, p2, Preeoral lobe (fixing organ, snout, proboscis). 7, Endostyle. A.A. Prvoral pit or proboscis-pore. #. Mouth. 2%. Neuropore. wc. Medullary tube, o%, Noto- chord, ¢ Eye. of Otocyst. ov. and 4, Proboscis-gland and proboscis-heart of s Balanoglossus 276 K ooo AW ood BS a ta Oo ‘aia a4, holo B ‘] 0? Fig. 132. — Sagitta hexaptera from the ventral surface ; nearly three times natural size. (After O. HERTWIG.) a. Anus. écl, Head-cavities. dc, Trunk-ceelom. 6c3, Caudal caslom. ¢./. Caudal septum. com, Commissure, from the cerebral ganglion to the single ventral ganglion. /1, 72, 78. Fins. m. Mouth. od, Oviduct. ov, Ovary. 5p. Prehen- sile bristles. s.v. Seminal vesicle. ¢, Tes- tis. v.g. Ventral ganglion. THE PROTOCHORDATA. neural tube into the extreme posterior end of the aliment- ary canal; in fact, into that portion of it which, in the embryos of the higher forms, is known as the post-anal gut. The anterior neuren- teric canal, in its most primi- tive condition, opens into the base of the buccal tube (Fig. 131). On this account we find in the Ascidian tadpole that the mouth is no longer ven- tral, as itis in Balanoglossus, but is placed dorsally, im- mediately in front of the anterior extremity of the medullary tube. This timate relation between the in- mouth and the central ner- vous system gives a reason for the contrast between the dorsal position of the mouth in the Ascidian tadpole and its ventral position in Bala- noglossus. In Amphioxus we have seen that the mouth has been forced aside from its more primitive dorsal position by the forward extension of the notochord to the tip of the PREORAL LOBE. 277 preoral lobe. The origin of the main cavity of the pre- oral lobe in Amphioxus from the right of a symmetrical pair of head-cavities (anterior intestinal diverticula of Hatschek) has been described in a previous chapter. In Balanoglossus there is no such complete division of the preoral body-cavity, but it is throughout a single space, its right and left halves being confluent. If we now com- pare the condition of things in the embryo of Amphioxus, where we have a symmetrical pair of head-cavities, with that of some other form which, in the adult condition, possesses a distinct pair of such cavities, it may assist us in imagining how the mouth could have assumed such opposite relations as have been mentioned above. But first it may be pointed out that in Appendicularia, where, as it would appear, in correlation with the second- ary acquirement of a purely pelagic habit of life (although this point of view is not shared by such authorities as Herdman, Seeliger, and Brooks), the preoral lobe has been reduced to a minimum, or to zero, the mouth has thereby come to lie in a terminal, or sub-terminal, position, with a slight tendency towards the dorsal side.* In the curious pelagic worm, Sagitta2, we meet with another instance of an animal in which the przoral lobe, in the ordinary sense of the term, is reduced to a mini- mum, and the mouth has therefore a sub-terminal position, with a ventral inclination (Fig. 132). But although there is no distinct praoral lobe in Sagitta, there is, neverthe- less, a pair of head-cavities, which are directly comparable, if not perfectly homologous, with the above-mentioned * Whatever the truth may be as to the precise systematic position and phylogenetic value of Appendicularia, one thing, to my mind, remains abso- lutely certain, namely, that it has descended from a form which possessed a preoral lobe, and that it has secondarily lost that structure. 278 THE PROTOCHORDATA. head-cavities of Amphioxus, although they have a some- what different origin. It should not be forgotten that Sagitta occupies a very isolated position in the zodlogical system, being placed in a group by itself, the Chetoguatha, and that therefore the peculiarities of its organisation cannot be taken as repre- senting any definite intermediate stage in the phylogeny of other forms, yet, from a general standpoint, the con- ditions which it presents in its life-history are highly instructive, The head-cavities of Sagitta arise by constriction from the anterior extremities of the single pair of archenteric pouches which give rise to the ccelom of the adult. They remain distinct and separate on either side of the head throughout life. If, now, we imagine them to grow for- ward and fuse together in front of the mouth, in a simi- lar manner to that described above for the enteroccelic pouches of Asterias, we should have a preoral body-cavity of a similar character to that of Balanoglossus. Now, the ultimate position of the mouth under these new conditions would depend upon circumstances affect- ing the whole organisation of the animal. In an animal whose grade of organisation was on an approximate level with that of Sagitta the mouth would undoubtedly remain on the ventral side of the body. But in an animal whose organisation had reached the stage of evolution represented by that unknown ancestor of Amphioxus (most nearly represented at the present time by the Ascidian tadpole), whose notochord did not extend beyond the anterior limit of the neural tube, the mouth would pass to the dorsal side of the body to come into connexion with the neural canal. PREORAL LOBE. 279 THE PRHORAL LOBE IN THE CRANIATE VERTEBRATES. After what has been said above, in this and the preced- ing chapters, the question as to how the przoral lobe is represented in the craniate Vertebrates need not detain us long. Since, as shown above, the nervous element of the pre- oral lobe (apical plate and cerebral ganglion) is entirely lacking in the Vertebrates, we can only expect to find the mesodermal element represented in the head-cavities of the higher forms. In consequence of the great development of the brain, even in the lowest craniate Vertebrates, as compared with Amphioxus, and in consequence too of the cranial flexure, the head-cavities have been made to assume a more sub- ordinate position, and no longer take part in the formation of a prominent lobe in front of the body. This is a perfect illustration of “le principe du balancement des organes”’ of Geoffroy Saint-Hilaire, the przoral lobe decreasing as the brain increases. A comparison between Figs. 70, 72, 117, and 135 will show at once that the przoral head- cavities of Amphioxus and Balanoglossus are the homo- logues of the premandtbular head-cavities of the craniate Vertebrates. These cavities lie at first below the mid-brain, and later their walls give rise to most of the eye-muscles. In Figs. gt and 135 the median portion of the pramandibular cavities can be seen still in the form of an anterior pocket of the endoderm, and it may be noticed how far it is removed from the anterior extremity of the body to which it extends in Amphioxus, etc. In the craniate Verte- brates the brain extends forwards, and the head-cavities 280 THE PROTOCHORDATA. remain behind. This is, as we should expect, the exact reverse to what obtains in Amphioxus. In connexion with the evolution of the przoral lobe, we thus have an excellent example of repeated change of function. We may conclude, therefore, that the przoral lobe, which, in the /zvertebrates, is above all the bearer of the cerebral ganglion, and in the Protochordates is released from this function and becomes in part a locomotor (Balanoglossus, Cephalodiscus) fixing (Ascidian) and bur- rowing (Amphioxus) organ, is represented in the craniate Vertebrates by the premandibular head-cavities, whose walls give rise to most of the eye-muscles. THE MOUTH OF THE CRANIATE VERTEBRATES. In consequence of the increase in the size of the brain, its forward extension and its cranial flexure, together with the relative reduction of the head-cavities, it is obvious that the mouth has been carried round from its primitively dorsal position to its final position on the ventral side of the head in the craniate Vertebrates. (Cf. Fig. 91.) This would have been all that need be said about the mouth were it not for the fact that the view, originally started by Dourvn, that the Vertebrate mouth was a new formation resulting from the fusion of two gill-slits, has received such wide support and still in a measure holds its own. Since the Annelid mouth perforates the central nervous system in passing through the circumcesophageal nerve- collar, it was necessary to frame a theory which would get over the difficulty that nothing of the kind occurs in the Vertebrates. Accordingly Dohrn supposed that the old Annelid mouth had become aborted, and was replaced MOUTH. 281 by a new mouth derived from a fusion across the mid- ventral line of a pair of gill-clefts. DouRN was a trifle uncertain as to the rudiment of the old mouth, but BEARD was more certain on this point, and thought he had estab- lished the fact that the hy- pophysis cerebri represented the remains of the old An- nelid mouth. Dohrn certainly succeeded in bringing forward some apparently good evidence in support of his theory of the gill-slit origin of the mouth. This evidence was derived from the study of the de- velopment of the mouth in Teleostean or bony fishes. Fig. 133. — Two frontal views of an embryo of Batrachus tau, to show the In many Teleosteans the mouth has at first an appar- ently double origin, in that two separate ectodermal in- growths occur which fuse with the endoderm, instead of the median stomodceal involution which is so char- acteristic of other Verte- brates. This double origin double nature of the stomodceum. (From hitherto unpublished drawings kindly lent by Miss C. M. CLAPP.) The embryo is lying upon the yolk, and the septum which divides the stomo- dceum passes from the upper lip to the surface of the blastoderm which covers the yolk. The lower figure is a drawing of the same embryo as the upper, a few hours later. Above the stomodceum are seen the small nasal pits (rudiments of the external nares), and at the sides of the head are the rudiments of the eyes. of the mouth is particularly well shown in the embryos of the remarkable toad-fish, Batrachus tau, as observed by Miss CorneLIA CLAPP at the Marine Biological Laboratory of Woods Holl, Mass., in 1889 (Fig. 133). In this case the mouth-cavity is seen to be divided into two halves by a median septum. Subsequently the septum becomes absorbed, and the 282 THE PROTOCHORDATA. two halves of the mouth coalesce. In view of the pre- vious existence of the gill-slit theory of the mouth, some such theory being a necessary accessory to the Annelid- theory, it is not surprising that this undoubted double origin of the mouth in Teleosteans should be regarded as a striking confirmation of Dohrn’s hypothesis. And yet, occurring as it does only in the Teleosteans, whose devel- opment is admittedly in many respects highly modified, the interpretation which Dohrn and his followers have placed upon this observation must always have been open to doubt. The simplest explanation of the double origin of the Teleostean mouth is that, owing to certain condi- tions (possibly mechanical) of development, the two angles of the mouth develop before the median portion. This is the conclusion which H. B. PotLarp has also reached in his recent studies on the development of the head in the Teleostean fish, Godzus captto. According to the standpoint I have adopted in the fore- going pages, there is no @ frtorz reason for doubting that the Vertebrate mouth is completely homologous with the Protochordate mouth; and that the latter in its turn is the direct descendant of the typical Invertebrate mouth. Again, the anatomy and development of the Protochor- dates and of the Cyclostomi (Ammoccetes) show no indica- tion whatever of a discontinuity in the evolution of the most highly elaborated mouth of the gnathostomous or jawed Vertebrates. We conclude, therefore, that the ventral mouth of the craniate Vertebrates is the homologue of the primordial dorsal mouth as we find it in the Protochordates, and that its direction of evolution has been, as was so ably main- tained by Ba.Frour, from the cyclostomous to the gnatho- stomous condition. HYPOPHYSIS. 283 SIGNIFICANCE OF THE HYPOPHYSIS CEREBRI. The pituitary body, or hypophysis, belongs to the series of ductless “glands” (pineal body, thyroid gland, thy- mus, etc.) which are such a characteristic feature of the vertebrate organisation. It arises as an ectodermal invo- lution from the roof of the stomodceum, directed towards the base of the primary fore-brain, from which the infun- dibulum grows out. The pituitary involution becomes in most forms nipped off from the stomodceum, and then lies as a closed sac in contiguity with the infundibulum. Later on it produces a system of branches, the lumina of which tend to dis- appear; and in some forms (e.g. Mammalia) it undergoes actual fusion with the infundibulum. The very constant relation of the hypophysis to the infundibulum in the craniate Vertebrates (see Fig. 134) naturally led to the supposition that there must originally have been a functional connexion between the two struct- ures of a similar nature to that which exists between the olfactory pit and neuropore in Amphioxus. Recent re- searches, however, have rendered it probable that such a supposition is erroneous. Von KupFrFer has discovered the homologue of the lobus olfactorius of Amphioxus in the craniate Vertebrates, and has shown that it occurs at a point far removed from the infundibular region. Until recently it was also very generally thought that the infundibulum represented the anterior end of the brain, which had become bent downwards and backwards by the cranial flexure. Kupffer, however, has brought for- ward weighty reasons for doubting this view. According to him, the infundibulum is essentially a downgrowth or 284 THE PROTOCHORDATA. evagination from the floor of the brain, occurring behind the anterior terminal extremity of the brain. It follows that the morphological anterior extremity of the craniate brain coincides with the median Jodus olfac- torius tmpar, which also represents the point of last con- nexion of the medullary tube with the superjacent ecto- derm. The lobus olfactorius impar lies in the anterior vertical wall, which forms the boundary of the primary fore-brain in front, known as the Jamzna terminalis. RaBL- Ruckuarp has also observed the median olfactory lobe in Fig. 134. — Sagittal section through the head of an embryo of Acanthias. (After RABL-RUCKHARD.) a.c. Position of anterior commissure. a/, Alimentary canal. ce7. Cerebellum. ch. Notochord; the black shading below the notochord indicates the aorta. fo. Fore-brain, 4.6, Hind-brain. Ay. Hypophysis, already shut off from the stomodceum and lying as a closed sac at the base of izf the infundibulum. Zo. Lobus olfactorius. . Mouth. m.d, Mid-brain. o.c. Optic chiasma. 2.d. Pineal body (epiphysis). the Selachian embryo (Fig. 134), and it has since been found by BuRCKHARDT in other forms. It can thus hardly be doubted that the median rudi- mentary olfactory lobe of the embryos of the higher Vertebrates is homologous with the lobus olfactorius of Amphioxus (Fig. 51), and, like the latter, represents the remains of the neuropore. In Amphioxus, however, the HYPOPHYSIS. 285 olfactory lobe abuts against the olfactory pit, and, in fact, in young individuals opens into it by the neuropore (Fig. 45). On the view which I have urged above, that the olfactory pit of Amphioxus is homologous with the hypophysis cerebri of the craniate Vertebrates, it must be assumed that in the latter forms, the neuropore hav- ing ceased to be in any way a functional organ, the hy- pophysis, which has likewise become (morphologically) a vestigial structure, has been mechanically separated from the neuropore, with which it was primitively in functional connexion. It must be supposed that this separation of the hypophysis from the neuropore has been effected by the more rapid downward growth of the ectoderm (from which the hypophysis arises) than of the wall of the brain, so that the hypophysis has been carried farther round to the lower side of the head than the neuropore (Fig. 135). The reason for this unequal growth of the external body- wall and of the cerebral wall may, perhaps, be sought for in the great and independent increase in the cubical con- tents of the brain.® We thus arrive at the conclusion that the present relation of the hypophysis to the infundibulum in the craniates, however intimate it may be in some cases, is, nevertheless, incidental and secondary. That this conclusion is not so strained as might appear at first sight is clearly shown by the fact that the in- fundibulum is not the only structure with which the hypophysis enters into close relations. In the exceptional cases of Myxine and Bdellostoma, for instance, the distal end of the hypophysis has nothing to do with the infundibulum, but actually opens into the pharynx. In these hag-fishes, as also in the lamprey 286 THE PROTOCHORDATA. (where there is no internal opening of the hypophysis into the pharynx), the external opening of the hypophysis does not close up, as in the higher forms, but persists throughout life, becoming carried round to the top of the head during the embryonic development by differ- ential growth of neighbouring parts, as has been actually observed in Petromyzon. Fig. 135.— Median sagittal section through the head of young Ammoceetes. (After KUPFFER.) The arrow indicates the extent to which the hypophysis has been (hypothetically) removed from the neighbourhood of the neuropore (lobus olfactorius impar). ch, Notochord. ec. Ectoderm. ex. Endoderm. ef. Epiphysis. Ay. Hypo- physial involution. Zo, Lobus olfactorius impar. 7. Nasal involution. gm. Me- dian portion of preemandibular cavity. s¢, Stomodcum, F.A/.4. Primary fore-, mid-, and hind-brain. In other cases, as, for example, in the embryo of the rabbit, it has been observed that the hypophysis actually undergoes a temporary fusion with the front end of the notochord; and in all cases the distal end of the hypophysis grows inwards as much towards the notochord as towards the infundibulum, so that for the embryonic stages of the craniate Vertebrates it might be said that the relations of HYPOPHYSIS. 287 the hypophysis to the front end of the notochord are as con- stant as its relations to the infundibulum. So close is the apparent relation of the hypophysis to the notochord that at least one zoologist, HuBRECcHT, has suggested that there was originally a functional connexion between the two structures. Again, in the embryo of Acztpenser, the sturgeon, as shown by Kuprrer, the distal end of the hypophysis undergoes temporary fusion with the subjacent wall of the alimentary cavity. In spite of the extremely modified character of the embryo of Acipenser (the embryo being flattened out like a disc over the yolk), Kupffer regards this fusion of the hypophysis with the endoderm as being of great morphological significance. On the contrary, for the reasons mentioned above, I would regard all these fusions of the hypophysis in the craniate Vertebrates, whether with the infundibulum, notochord, or endoderm, as being of an entirely incidental character, often due, perhaps, to a tendency of such con- tiguous embryonic tissues to fuse together. I therefore suggest that: The hypophysis arose in con- nexion with a functional neuropore, when the neuropore ceased to be functional, there was no longer any bond of union between tts inner portion, which opened into the cerebral cavity, and tts outer portion, which opened into the buccal cavity; and these two portions became separated by differential growth of the cerebral and body-walls (cf. Fig. 135). The Ascidian Hypophysts. The development of the hypophysis in a typical As- cidian, its constriction from the wall of the cerebral vesicle in the form of a tube, and its opening into the 288 THE PROTOCHORDATA. buccal cavity, or branchial sac, have been described above. The most serious objection which has been raised against the comparison of the hypophysis of the Ascidians with that of the craniate Vertebrates is, that in the former the hypophysis opens, not at an ectodermal surface into the stomodceum, but at an endodermal surface (behind the stomodceum) into the branchial sac. This is undoubtedly the case in some Ascidians, e.g. Drstaplia, and probably also in Clavelina, etc. In Czona, however, as I can state after renewed study of the question, it apparently opens at first into the buccal cavity precisely in the line of junction between the stomodceum and the branchial sac, so that its upper margin is continuous with the stomodceal epithelium, while its lower margin is continuous with the epithelium of the branchial sac. It is probable that too much stress has been laid on the question whether the hypophysis of the Ascidians opens at an endodermic or at an ectodermic surface, and that thus the attention has been diverted from the essential fact that the hypophysis opens into the buccal tube at the entrance to the branchial sac. In the case of the Ascid- ians, therefore, I should also regard the fusion of the hypophysis, whether with the ectoderm of the stomodceum or with the endoderm of the branchial sac, as being in itself non-essential, while the actual opening of the hy- pophysis (itself derived by constriction from the nerve- tube) into the buccal cavity, apart from the question of an ectodermal or endodermal surface, is the essential point. CONCLUSION. 289 CONCLUSION. From the facts that have been recorded and the consid- erations that have been urged in these pages, it would follow that one of the chief factors in the evolution of the Vertebrates has been the concentration of the central nervous system along the dorsal side of the body (in contrast to the position of the longitudinal nerve-cord of Annelids, etc., along the ventral or /ocomotor surface), and its conversion into a hollow tube. If it be admitted that the hypophysis became evolved in connexion with a func- tional neuropore, it is obviously a structure which has arisen within the limits of the Vertebrate phylum, and can, therefore, have no representative in the typical Invertebrate organisation. It has been suggested by ADAM SEDGWICK and vAN Wine that the original function of the central canal of the spinal cord was to promote the respira- tion (oxygenation) of the tissue of the central nervous system, water entering by the neuropore, and passing out through the posterior neurenteric canal. It is not so easy to form a conception as to the prime origin of the other two cardinal characteristics of a Vertebrate (Chordate); namely, gill-slits and notochord. As to the origin of gill-slits, it has been suggested inde- pendently by Harmer and Brooks, that they arose at first not so much to perform the direct function of respiration, as to carry away the bulk of the water which constantly entered the mouth with the food, so as to avoid the neces- sity and discomfort of the never-ceasing flow of water through the entire length of the alimentary canal. In Cephalodiscus, for example, the luxuriant branchial plumes must be sufficient for the respiration of the minute animal, 290 THE PROTOCHORDATA. while the usefulness of the pair of gill-slits, in allowing the surplus water to pass out of the pharynx, is evident. The notochord is more difficult to explain, and the fact of its occurrence in the proboscis of Balanoglossus and in the tail of the Ascidian tadpole is very puzzling. The mode of its occurrence in Balanoglossus is undoubtedly divergent, and not in the direct line of Vertebrate descent. It is possible that the notochord has not arisen through a process of elaborate change of function from a pre-existing structure, but simply as a solidification of the endoderm which was continued into the caudal or post-anal extension of the body to form the axial support for a locomotor tail ; while the subsequent extension of the notochord into the pree-anal region of the body is not difficult to understand. The general capacity of the endoderm for producing skeletal tissue is already present in some of the Medusze and Hydroid polyps whose tentacles are stiffened by a solid endodermal axis. From a purely morphological point of view it now seems as though the przoral lobe and in a lesser degree, perhaps, the hypophysis, would materially assist in furnish- ing the key to a correct appreciation of the relationship between the craniate Vertebrates, the Protochordates, and the Invertebrates. As we have indicated above, in the formulation of the Annelid-theory* no allowance has been made for the prin- ciple of parallelism in evolution; but it is impossible to doubt that this is a very potent factor which should always be borne in mind in estimating the genetic affinity between widely different groups of animals. The closer the super- ficial resemblance between an Annelid and a Vertebrate (in the possession of somites, segmental organs, etc.) is shown to be, the more perfect appears the parallelism CONCLUSION. 291 in their evolution and the more remote their genetic affinity. For the present we may conclude that the proximate ancestor of the Vertebrates was a free-swimming animal intermediate in organisation between an Ascidian tadpole and Amphioxus, possessing the dorsal mouth, hypophysis, and restricted notochord of the former; and the myo- tomes, ccelomic epithelium, and straight alimentary canal of the latter. The ultimate or primordial ancestor of the Vertebrates would, on the contrary, be a worm-like animal whose organisation was approximately on a level with that of the bilateral ancestors of the Echinoderms. NOTES. I. (p. 246.) For the discussion of the phenomena of meta- merism and the enumeration of examples of independent metameric repetition of parts, consult the following: Lanc, ARNOLD. Der Bau von Gunda Segmentata und die Verwandtschaft der Plathel- minthen mit Celenteraten und Hirudineen. Mitth. Zool. Stat. Neapel, Bd. III. 1882. p.187 e¢seg. SEDGWICK, ADAM. On the Origin of Metameric Segmentation, and Some Other Mor- phological Questions. Quarterly Jour. Micro. Sc. XXIV. 1884. pp. 43-82. Bareson, WittiaM. Zhe Ancestry of the Chordata. Quarterly Jour. Micro. Sc. XXVI. 1886. pp. 535-571. CALD- WELL, H. Slastopore, Mesoderm, and Metameric Segmentation. Quarterly Jour. Micro.Sc. XXV. 1885. pp.15-28. HUBRECHT, A.A.W. Report on the Nemertea collected by H. M.S. Challenger, 1873-76. Chall. Rept. Zodl. XIX. 1886. (Also, HUBRECHT. The Relation of the Nemertea to the Vertebrata. (Quarterly Jour. Micro. Sc. XXVII. 1887. pp. 605-644.) Wan BENEDEN, Epouarp. Recherches sur le Développement des Arachnactis. Contribution a la Morphologie des Cérianthides. Archives de Biologie, XI. 1891. pp. 115-146. Also consult the recent great work of Bateson, Mavrerials for the Study of Variation. London, 1894. 292 THE PROTOCHORDATA. 2. (p. 273.) On the subject of the preoral lobe and the api- cal nervous system of Invertebrates, see the following: BALFour, F. M. Comparative Embryology. 1881. Vol. II. Chap. 12. Observations on the Ancestral Form of the Chordata. BEarD, J. Zhe Old Mouth and the New, A Study in Vertebrate Mor- phology. Anat. Anz. III. 1888. pp. 15-24. Wison, E. B. The Embryology of the Earthworm. Jour. Morph. III. 1889. pp. 387-462. Harscuex, B. Lehrbuch der Zoologie. 3d Liefer- ung. Jena, 1891. Wittey, A. On the Evolution of the Preoral Lobe. Anat. Anz. IX. 1894. pp. 329-332. 3. (p. 285.) From what has been said in the text, it is obvious that the hypophysis of the craniate Vertebrates, in becoming separated from the neuropore, has retained (at least in the embryo) its primitive relations with the buccal cavity, and, like the latter, has been made to assume its present position in consequence of the forward growth of the brain and the ensuing cranial flexure. In Amphioxus, the hypophysis (.e. olfactory pit) arises as an ectodermic involution immediately over the neuropore, but still independent of the latter. In other words, the neuropore exists in Amphioxus for a considerable length of time before the hypoph- ysis forms ; and this is in accordance with what we should expect from the analogy of the craniate Vertebrates. In the Ascidians, however, the conditions are somewhat different, and there is at first no such obvious differentiation between neuropore and hypoph- ysis. For the simple Ascidians (¢.g. Ciona) it must at present remain doubtful whether the increase in size of the hypophysis takes place entirely by interstitial growth, or whether there is any ingrowth from the wall of the buccal tube at the lips of the aper- ture (dorsal tubercle) of the hypophysis. In any case there are not wanting indications in the Ascidians of a distinction, and even separation, between the distal portion of the hypophysis, which at first opens into the cerebral vesicle, and the proximal portion, which opens into the buccal cavity. In the adult, the proximal portion of the hypophysis has the form of a simple duct, opening by the so-called dorsal tubercle into the buccal cavity, while the subneural gland arises as a proliferation from the ventral wall of the distal portion. In Phallusia mammillata, as was discovered by Juuin (Archives de Biologie, 11. 1881. pp. 211-232), num- NOTES. 293 bers of secondary tubules grow out from the principal duct of the hypophysis, and acquire ciliated funnel-like openings into the peribranchial chamber ; subsequently HerpMan (Proc. Roy. Soc. Lidinburgh, XII. 1882-84. p. 145) found that in this form the dorsal tubercle, or opening of the hypophysis into the buccal cavity, is sometimes absent. In Czona intestinalis 1 have found in young individuals an obliteration of the lumen of the hypophysis between the proximal and the distal portions. In other cases, as in Appen- dicularia, the glandular portion of the hypophysis may be reduced or absent. On the subject of the Ascidian hypophysis, the following papers should also be consulted: SHELDON, Litian. Vote on the Ciliated Pit of Ascidians and its Relation to the Nerve-ganglion and So- called Hlypophysial Gland. Quarterly Jour. Micro. Sc. XXVIII. 1888. pp.131-148. Hyort, Jouan. Ueber den Entwicklungs- cyclus der Zusammengesetsten Ascidien. Mitth. Zool. Stat. Neapel, X. 1893. pp. 584-617. Mercatr, Maynarp M. Zhe Eyes and Subneural Gland of Salpa. Baltimore, 1893. (Published as Part IV. of Professor Brooks’s Monograph of the Genus Salpa.) 4. (p. 290.) The most complete presentation of the Annelids- theory is contained in the classical A/onographie der Capitel- liden des Golfes von Neapel, by Dr. Huco Etsic. It is needless to add that this monograph will command the gratitude and admiration of zodlogists to the end of time. = to REFERENCES. INTRODUCTION. Carus, J. VicToR. Geschichte der Zoologie. Miinchen, 1872. Dourn, ANTON. Der Ursprung der Wirbelthiere und das Prin- cip des Functionswechsels. Leipzig, 1875. HAECKEL, ERNST. Anthropogente oder Entwickelungsgeschichte des Menschen. Leipzig, 1874; 4th Edit., 1891. LANKESTER, E. Ray. Article “ Vertebrata.” Encycl. Brit., gth Edit. Republished in * Zodlogical Articles,” London, 1891. PERRIER, EDMOND. La Philosophie Zoologigue avant Darwin, 2d Edit. Paris, 1886. SEMPER, CARL. Dee Verwandtschaftsbeztehungen der geglieder- ten Thiere. Parts I. to II. Wiirzburg, 1875-76. I. anpD II. ANATOMY OF AMPHIOXUS.* ANDREWS, E. A. Zhe Bahama Amphioxus (preliminary ac- count). Johns Hopkins University Circulars. Vol. XII. p. 104. June. 1893. ANDREWS, E. A. dn Undescribed Acraniate: Asymmetron lucayanum. Studies from the Biol. Lab. Johns Hopkins Uni- versity, Vol. V. No. 4. 1893. pp. 213-247. Plates XIII.- XIV. Contains bibliography of systematic and faunistic works on Amphioxus. ANTIPA, GR. Ueber die Besiehungen der Thymus su den soge- nannten Kiemenspaltenorganen bet Selachiern. Anat. Anz. VII. 1892. pp. 690-692. One figure in text. * This bibliography does not by any means include all that has been written on the anatomy of Amphioxus. Some of the older and shorter works, as well as some of those relating to special points of histological detail, have been omitted, as they are fully dealt with in many of the memoirs here cited. 205 296 Io II 14 15 16 17 18 20 REFERENCES. BALFour, F.M. A Preliminary Account of the Development of the Elasmobranch Fishes. Quarterly Jour. Micro. Sc. XIV. N.S. 1874. pp. 323-364. Plates 13-15. Paper in which Balfour first published his discovery of the seg- mental origin of excretory tubules. This was made out also in the same year by Semper and Schultz. (Vide infra, Schztz.) BALFouR, F. M. Ox the Origin and History of the Urino- genital Organs of Vertebrates. Jour. of Anat. and Physiol. X. 1875. pp. 17-48. Eight figures in text. Amplification of his pre- vious work, with bibliography up to date. BALFour, F. M. The Development of Elasmobranch Fishes. Development of the Trunk. Jour. of Anat. and Physiol. XI. 1876. pp. 128-172. Plates 5 and 6. First account of origin of paired limbs from continuous epiblastic thickenings. Batrour, F. M. A Monograph on the Development of Elasmo- branch Fishes. London, 1878. BEDDARD, FRANK Evers. On the Occurrence of Numerous Nephridia in the Same Segment in Certain Earthworms, and on the Relationship between the Excretory System in the Annelida and in the Platyhelminths. Quarterly Jour. Micro. Sc. XXVIII. N.S. 1888. pp. 397-411. Plates 30-31. Contains discovery of neph- ridial network in Pericheta. BENHAM, W. BLAXLAND. Zhe Structure of the Pharyngeal Bars of Amphioxus. Quarterly Jour. Micro. Sc. XXXV.N.S. 1893. pp. 97-118. Plates 6-7. BOURNE, ALFRED GIBBS. Contributions to the Anatomy of the Hirudinea. Quarterly Jour. Micro. Sc. XXIV. N.S. 1884. Pp- 419-506. Plates 24-34. Contains discovery of nephridial network in Pontobdella. BOVERI, THEODOR. Ueber die Niere des Amphioxus. Miin- chener Medicin. Wochenschrift. No. 26. 1890. Sep. Abd. pp. I-13. Two figures in text. (Preliminary note.) BoveERI, THEODOR. Dre Nierencandlchen des Amphioxus. Ein Beitrag sur Phylogenie des Urogenitalsystems der Wirbelthiere. Zoolog. Jahrbiicher. Abth. fiir Morphol. V. 1892. pp. 429-510. Taf. 31-34 and five figures in text. Costa, O. GABRIELE. Cent zoologict ossia descrizione som- maria delle specte nuove di antmali discoperti in diverse contrade del regno nell’ anno 1834. Napoli, 1834. See also Fauna del regno di Napoli. 1839-50. CuEnoT, L. Etudes sur le sang et les glandes lymphatigues dans la série animale. Archives de zool. expérimentale, XIX. 1891. Amphioxus. pp. 55-56. 21 23 24 25 26 27 28 29 REFERENCES. 207 Notes absence of blood-corpuscles in Amphioxus. Those described by previous authors must therefore require another ex- planation. DOHRN, ANTON. Studien zur Urgeschichte des Wirbelthier- korpers. LV. Section 5. LEntstehung und Bedeutung der Thymus der Selachter. Mitth. Zool. Stat. Neapel. V. 1884. pp. 141-151. Taf. 8. Figs. 1 and 2. Eisic, Huco. Dze Segmentalorgane der Capitelliden. Mitth. Zool. Stat. Neapel. 1. 1879. pp. 93-118. Taf. IV. Discovery of numerous nephridia in single segments and an- astomoses between successive nephridia. EMERY, CARLO. Le specie del genere Fierasfer nel Golfo at Napoli. 2d Monograph in the “ Fauna und Flora des Golfes von Neapel.” Leipzig, 1880. EMERY, CARLO. Zur Morphologie der Kopfniere der Teleostier. Biologisches Centralblatt, I. 1881. pp. 527-529. See also Zoologischer Anzeiger, VIII. 1885. pp. 742-744. Fusari, Romeo. Bettrag sum Studium des peripherischen Nervensystems von Amphioxus lanceolatus. Internationale Mo- natsschrift fiir Anatomie und Physiologie, VI. 1889. pp. 120-140. Taf. VII.-VIII. Goopsir, JOHN. Ox the Anatomy of Amphioxus lanceolatus. Transactions of the Royal Society of Edinburgh, Vol. XV. Part I. 1841. pp. 241-263. GRENACHER, H. Bettrage zur nahern Kenntniss der Muscu- latur der Cyclostomen und Leptocardier. (Leptocardia proposed by Haeckel as a classificatory name on account of the simple tubular “heart” of Amphioxus.) Zeitschr. fiir Wiss. Zoologie, XVII. 1867. pp. 577-597. Taf. XXXVI. First isolation of muscle-plates of Amphioxus. GUNTHER, ALBERT. Synopsis of Genus Branchiostoma. In Report on Zodl. Collections of H. M.S. Alert. 1881-82. pp. 31- 33. London, 1884. HaTSCHEK, BERTHOLD. Die Metamerie des Amphioxus und des Ammocetes. Verh. Anat. Gesellschaft, 6th Versammlung. Wien, 1892. pp. 137-161. Eleven figures in text. 29 bis. HATSCHEK, BERTHOLD. Zur Metamerie der Warbelthiere. 30 Anat. Anz. VII. Dec. 1892. pp. 89-91. Huxvey, T. H. Preliminary Note upon the Brain and Skull of Amphioxus lanceolatus. Proceedings of the Royal Society, XXIII. 1874. pp. 127-132. Points out that in Myxine and Ammocceetes a velum is present separating the buccal (stomodceal) from the branchial cavity- 298 31 33 34 35 36 37 38 REFERENCES. The resemblance of the buccal cavity and tentacles (cirri) of Ammoceetes to the corresponding parts in Amphioxus is so close that there can hardly be any doubt the two are homologous. The anterior end of the nerve-tube of Amphioxus corresponds to the lamina terminalis of the craniate Vertebrates. Huxtey, T. H. Ox the Classification of the Animal Kingdom. Journal of the Linnzan Society (London), XII. 1876. pp. 199- 226. (Read 3d Dec., 1874.) Section on “epical,” p. 216 ef seg. Atrial cavity of Amphi- oxus and Ascidians is an epiccel like the opercular cavity of the Amphibian tadpole. KOLLIKER, ALBERT. Ueber das Geruchsorgan von Amphioxus. Miiller’s Archiv fiir Anat. Physiol., etc. 1843. pp. 32-35. Taf. II. Fig. 5. Discovery of olfactory pit and first description of the spermatozoa of Amphioxus. KOpPEN, Max. Beitrage sur vergleichenden Anatomie des Centralnervensystems der Wiorbelthiere. Zur Anatomie des Eidechsengehirns. Morphologische Arbeiten (Schwalbe), I. 1892. pp. 496-515. Taf. 22-24. Contains discovery of giant-fibres in caudal portion of spinal cord of Lacerta viridis. KouL, K. Einige Bemerkungen iiber Sinnesorgane des Amphi- oxus lanceolatus. Zool. Anz. 1890. pp. 182-185. States that sometimes there is a shallow olfactory groove on the right side as well as that in the left. Such grooves are often due to artificial crumpling, and the observation requires confirmation. KRUKENBERG, C. FR. W. Zur Kenntnis des chemischen Baues von Amphioxus lanceolatus und der Cephalopoden. Zool. Anz. 1881. pp. 64-66. See also HOPPE-SEYLER’S reply. pp. 185-187. Compare also CUENOT (supra). KUPFFER, CARL VON. Studien sur vergleichende Entwick- lunesgeschichte des Kopfes der Kranioten.L. Die Entwicklung des Kopfes von Acipenser sturio an Medianschnitten untersucht. 95 pp. 8°. 9g Tafeln. Miinchen und Leipzig, 1893. Contains also a chapter on brain of Amphioxus, with figures. LANGERHANS, PAUL. Zur Anatomie des Amphioxus lanceolatus. Archiv fiir mikroskopische Anatomie, XII. 1876. pp. 290-348. Taf. XII.-XV. Standard work on the histology of Amphioxus. LANKESTER, E. Ray. On Some New Points in the Structure of Amphioxus and thetr Bearing on the Morphology of Vertebrata. Quarterly Jour. Micro. Sc. XV. N.S. 1875. pp. 257-267. REVERENCE S. 299 39 LANKESTER, E. Ray. Contributions to the Knowledge of Amphi- oxus lanceolatus, Yarrell. \b., Vol. XXIX. 1889. pp. 365-408. Five plates. 4o Lworr, Basttius. Uber den Zusammenhang von Markrohr und Chorda betm Amphioxus und ahnliche Verhaltnisse bet Anneliden. Zeitschrift fur wiss. Zoologie. Bd. 65. 1893. pp. 299-308. Taf. XVII. Describes those supporting fibres of the spinal cord of Amphi- oxus which descend in successive paired groups to the notochordal sheath and penetrate the latter in order to insert themselves on the inner surface of the sheath. The openings in the notochordal sheath of Amphioxus, through which the ventral supporting fibres pass, were first observed by WILHELM MULLER in 1871. (W. MUuvter, Ueber den Bau der Chorda dorsalis. Jenaische Zeit- schrift, VI. 1871. pp. 327-354.) See also PLatr (infra) and Lworr (88). Latter contains complete bibliography of literature relating to structure of notochord. 41 Maver, Paut. Ober dic Intwicklung des Herzens und der grossen Gefassstimme bet den Selachiern. Mitth. Zool. Stat. Neapel. VII. 1887. pp. 338-370. ‘Taf. 11-12. 42 Mever, Epuarp. Studien iiber den Korperbau der Anneliden. Mitth. Zool. Stat. Neapel. VII. 1887. pp. 592-741. Taf. 22-27. 42 bis. Mortiau, CAMILLE. Recherches sur la Structure de la Corde dorsale de CAmphioxus. Bull. Acad. Belg. Tome 39. No. 3. 1875. 22 pp. One plate. 43 Muitver, Wituetm. Ueber adie Stammesentwicklung des Sehorgans der Wirbelthiere. 76 pp. Five plates. 4°. Leipzig, 1874. 44 MULLER, WituneLM. Ceber das Urogenttalsystem des Amphi- oxus und der Cyclostomen. Jenaische Zeitschr. fiir Naturwissen- schaft, Bd. Il. (neue Folge). 1875. Sep. Abdruck. pp. 1-38. Two plates. This is the important work in which the pronephros and mesonephros were for the first time clearly distinguished from one another. The author was, however, in error regarding Johannes Miiller’s renal papillae of Amphioxus. 45 Murr, Jouannes. Uber den Bau und die Lebenserscheinun- gen des Branchiostoma lubricum Costa, Amphioxus lanceolatus, Varrell. Berlin, 1844. 4°. 40 pp. Five plates. Read at the kénigl Akademie, 1841. 46 NANsEN, Fripryor. Zhe Structure and Combination of the His- tological Iklements of the Central Nervous System. Bergens Museums Aarsberetning for 1886. Bergen, 1887. 300 REFERENCES. 47 OwsJANNIKOW, Puitip. Ueber das Centralnervensystem des Amphioxus lanceolatus. Bulletin de l’Acad. imp. des Sciences de St. Pétersbourg, Tome XII. 1868. pp. 287-302, with one plate. Also in Mélanges Biologiques, T. VI. pp. 427-450. Introduced a method of maceration by which he was able to shake out the central nervous system and thus isolate it from the body. In this way he was able to correct the erroneous descrip- tions of de Quatrefages and others (who stated that there were ganglionic enlargements in the spinal cord), and to discover the alternate arrangement of the spinal nerves. 48 PLaTT, JULIA B. Frbres connecting the Central Nervous System and Chorda in Amphioxus. Anat. Anz. VII. 1892. pp. 282-' 284. Three figures in text. 49 POLLARD, E. C. A Mew Sporozoin in Amphioxus. Quarterly Jour. Micro. Sc. XXXIV. N. S. 1893. pp. 311-316. Plate XXIX. Unicellular parasites in intestinal epithelium. 49 67s. PoucHET, GEorGES. On the Laminar Tissue of Amphioxus. Quarterly Jour. Micro. Sc. XX.N.S. pp. 421-430. Plate XXIX. 50 DE QUATREFAGES, ARMAND. AZémoire sur le systéme nerveux et sur Vhistologie du Branchiostome ou Amphioxus. Annales des sciences nat. Zoologie. 3d series. IV. 1845. pp. 197-248. Plates 10-13. First observation of passage of ova through atriopore; and discovery of the peripheral ganglion-cells in connexion with the cranial nerves. 51 RATHKE, HEINRICH. Bemerkungen iiber den Bau des Amphi- oxus lanceolatus, eines Fisches aus der Ordnung der Cyclostomen. Konigsberg, 1841. 4°. pp. 1-38. One plate. 52 ReEtzius, Gustav. Zur Kenntniss des centralen Nervensystems von Amphioxus lanceolatus. Biologische Untersuchungen. Neue Folge II. pp. 29-46. Taf. XI.-XIV. Stockholm, 18go. 52 60s. RETzIUS, GusTAv. Das hintere Ende des Riickenmarks und sein Verhalten zur Chorda dorsalis bet Amphioxus lanceolatus. Verh. Biol. Vereins. (Biologiska Foreningens Forhandlingar.) Stockholm. Bd. IV. pp. 10-15. 9 figs. 1891. 53 RouDE, Emit. A‘stologische Untersuchungen tiber das Nerven- system von Amphioxus lanceolatus. In Anton Schneider's Zoo- logische Beitrage. Bd. II., Heft 2. Breslau, 1888. pp. 169-211. Plates XV.-XVI. Standard work on the central nervous system of Amphioxus. 54 Ronon, JOSEF Victor. Untersuchungen iiber Amphioxus lanceolatus. Lin Beitrag zur vergleichenden Anatomie der Wir- 55 56 57 58 59 60 61 REFERENCES. 301 belthiere. In Denkschriften der Math.-Naturwiss. Classe der kais. Akad. der Wissenschaften. Bd. XLV. Wien, 1882. 64 pp. 4°. Six plates. Relates chiefly to nervous system. Describes also the smooth muscle-fibres in wall of pharynx, etc. Finds that the majority of sensory nerve-fibres to the skin end freely between the cells of the ectoderm in bush-like ramifications. For the rest, see NANSEN ROHDE, RETZzIUS, and FuSARI. Ropu, W. Untersuchungen iiber den Bau des Amphioxus lanceolatus. Morphologisches Jahrbuch, II. 1876. pp. 87-164. Taf. V.-VII.; also figures in text. RUCKERT, JOHANNES. Lutwickelung der Excretionsorgane. Ergebnisse der Anatomie und Entwicklungsgeschichte (Merkel und Bonnet), 1. 1891. pp. 606-695. Includes an extensive bibli- ography. SCHNEIDER, ANTON. Settrage zur vergleichenden Anatomie und Entwicklungsgeschichte der Wrorbelthiere. lL. Amphioxus lanceolatus. pp. 3-31. Taf. XIV.-XVI. 4°. Berlin, 1879. SCHULTZ, ALEXANDER. Zur Entwickelungsgeschichte des Sela- chieretes. Archiv. fiir Mikr. Anat. XI. 1875. pp. 569-580. Taf. 34. Preliminary notes of both Semper and Schultz, regarding the segmental origin of the excretory tubules, were published in the Centralblatt fiir Medicinische Wissenschaft, 1874. SEMON, RICHARD. Studien tiber den Bauplan des Urogenital- systems der Wirbelthiere; dargelegt an der Entwickelung dieses Oregansystems bet Lchthyophis glutinosus. Jenaische Zeitschrift, XXVI. 1891. pp. 89-203. Taf. I1.-XIV. SPENGEL, J.W. Settrag zur Kenntniss der Kiemen des Amphi- oxus. Zool. Jahrbiicher. Abth. fiir Morphol. 1V. 1890. pp. 257- 296. Taf. 17-18. SPENGEL, J. W. Benham’s Krittk metner Angaben iiber die Kiemen des Amphioxus. Anat. Anz. VIII. 1893. pp. 762-765. STIEDA, LupwIG. Studien iiber den Amphioxus lanceolatus. Mém. de l’Acad. Impériale des Sciences de St. Pétersbourg, 7th series, Vol. XIX. No.7. 7o pp. Four plates. 1873. Contains some good observations on the central nervous system. First to show that the split-like structure above central canal did not correspond to the posterior fissure of the vertebrate spinal cord, but was a portion of the original central canal itself, the lumen of which had been partially obliterated by approximation of its walls. First identification of ventral (motor) roots of spinal nerves in Amphioxus. 302 63 64 65 66 67 68 69 REFERENCES. THACHER, JAMES K. Aedian and Paired Fins ; a Contribution to the History of Vertebrate Limbs. Transactions Connecticut Academy, III. No. 7. 1877. pp. 281-310. Plates 49-60. WEISS, F. ERNEST. Excretory Tubules in Amphioxus lanceolatus. Quarterly Jour. of Micro. Sc. XXXI. N.S. 1890. pp. 489-497. Plates 34-35. VAN WIJHE,J.W. Ueber Amphioxus. Anat. Anz. VIII. 1893. pp. 152-172. VAN WIJHE, J. W. Due Kopfregion der Cranioten beim Amphi- oxus, nebst Bemerkungen iiber die Wirbeltheorte des Schédels. Anat. Anz. IV. 1889. pp. 558-566. VAN WIJHE,J.W. Ueber die Mesodermsegmente des Rumpfes und aie Entwicklung des Excretionssystems bet Selachiern. Archiv. f. Mikr. Anat. XXXIII. 1889. pp. 461-516. Taf. 30-32. WILLEY, ARTHUR. LRefort on a Collection of Amphioxus, made by Professor A. C. Haddon, in Torres Straits, 1888-89. Quarterly Jour. Micro. Sc. XXXV.N.S. January, 1894. pp. 361-371. One figure in text. Branchiostoma cultellum. Peters. III. DEVELOPMENT OF AMPHIOXUS. Ayers, HowarpD. Sdellostoma Dombeyt,Lac. A Study Srom the Hopkins Marine Laboratory. Biological Lectures, Marine Biological Laboratory, Woods Holl. 1893. No. VII. Boston, 1894. 69 ds. BERT, PAUL. On the Anatomy and Physiology of Amphioxus. Annals and Mag. of Nat. Hist., 3d Series. Vol. XX. 1867. pp. 302-304. (Translated from Comptes Rendus. Aug. 26th, 1867. pp. 364-367.) Breeding season of Amphioxus at Arcachon is from March to May. Was the first to observe the ejection of the sperm through the atriopore. Calls attention to remarkable lack of regenerative power in Amphioxus. Individuals cut in two will live for several days, but will not regenerate. “If the extremity of the body of an Amphioxus be cut off, the wound does not cicatrize; on the contrary, the tissues become gradually disintegrated. I have seen animals, with only the tail mutilated, become gradually eaten away up to the middle of the branchial region, and live thus without any intestines, without abdominal walls, and without branchiz for several days.” These observations of Paul Bert are “I bo “I wn “I Ww “I ny DEFERENCES, 39 Oo capable of easy confirmation, and should be borne in mind in view of the extraordinary regenerative power which Wilson dis- covered in the segmentation Bovert, THEODOR. CU Ger titte der Geschlechts- ariisen und adie Entstehung der a TT beim Antiphi- exus. Anat. Anz. VII. 1892. pp. 170-81. Twelve figures. DOHRN, ANTON. Stedten sur Urgeschichte des Wrrbelthier- korpers. I. Die Entstehung und Bedeutung der Hy pophysts bet Petromyson Planert. Mitth. Zool. Stat. Neapel. IV. 832. DourN, ANTON. Studien, VII. Dre Thyreotdtea bet Petrosty- son, Amphtoxus und Tunicaten. Ib. VI. 1885. Dohrn lays unnecessary stress upon the fact that often in transverse section, especially in the anterior region of the pharynx, the endostyle of Amphioxus projects up into the cavity of the pharynx in the form of a convex lens-shaped ridge. This is merely due to the muscular contraction of the pharynx, which almost invariably takes place when Amphioxus is placed in a Killing reagent. It is, therefore, not an anatomical feature of any significance. DoHRN. ANTON. Studien, NI]. Zhyreotdea und Ay pobran- chialrinne, Spritslochsack und Pseudobranchtialrinne bet Fischen, Ammocetes und Tuntkaten. Wb. VII. 1887. Donrx, ANTON. Studien, NII. Cder Nerven und Gefiisse bet Ammocetes und Petromyson Planert. Ib. VUT. 1888. FRORIEP, AvuGUST. = Entivchelungyge des Kopfes Ergebnisse der Anat. und Entwickelungsg h (Merkel und Bonnet), I. Sgr. pp. 561-605. Eleven figures. Includes an extensive bibliography. HATSCHEK, BERTHOLD. Staten iider Entwreklung des Ant pire exus. Arbeiten a. d. Zool. Institute. Wein, 1881. 88 pp. Nine plates. HATSCHEK, BERTHOLD. Jttthetlungen tiber Amphroxus. Zoologischer Anzeiger, VII. 1884. pp. 517-520. Olfactory pit, sense-organ of proral pit, anterior preoral * nephridium.” HATSCHEK, BERTHOLD. Cer den Schichtenbau von Amphi- oxus. Anat. Anz. III. 1888. pp. 662-667. Five figures. ages of the embryo. ays oO va ig) Origin of sclerotome, ete. KASTSCHENKO, N. Zur Entwicklungsgeschi embryos. Anat. Anz. IIT. 888. pp. 445-467 One of the first to bring forward definite embryological facts to prove that the anterior (prve-auditory) head-cavities of VAN WIJHE (Ueber die Mesodermsegmente. ete., des Selachierkoptes. Amster- 304 80 81 83 84 85 86 REFERENCES. dam, 1882) are not homodynamous with the true somites. He was followed in this respect by RaBL (Theorie des Mesoderms. Morphologisches Jahrbuch, XV. 1889). KorscHELtT, E., und HEIDER, Kk. Lehrbuch der vergleichen- den Entwicklungsgeschichte der wirbellosen Thiere. 3a Heft. Jena, 1893. KOWALEVSKY, ALEXANDER. Lutwichlungsgeschichte des Am- phioxus lanceolatus. Mém. de Acad. Imp. des Sciences de St. Pétersbourg. VII. Series. T. XI. No. 4. 1867. Three plates. KOWALEVSKY, ALEXANDER. JVeitere Studien iiber die Ent- wicklungsgeschichte des Amphioxus lanceolatus, nebst einem Beitrage sur Homologie des Nervensystems der Wirmer und Wirbelthiere. Arch. f. Mikr. Anat. XIII. 1877. pp. 181-204. Two plates. Among the definite discoveries communicated by Kowalevsky in these two memoirs may be mentioned the following: General features of segmentation and gastrulation, origin of mesoderm from archenteric pouches, unique method of formation of nerve-tube (see text), origin of notochord, neurenteric canal, asymmetrical origin of gill-slits and mouth, and zz fart the metamorphosis. KUPFFER, CARL VON. Die Entwicklung von Petromyzon Planert. Arch. f. Mikr. Anat. XXXV. 1890. pp. 469-558. Six plates. Origin of head-cavities, hypophysis, etc. KUPFFER, CARL VON. Dre Entwicklung der Kopfnerven der Vertebraten. Verhandl. Anat. Gesellschaft in Miinchen. 18or. pp. 22-55. Eleven figures. (Erganzungsheft zum Anat. Anz. VI. 1891.) Ammoceetes (see Fig. 92 in text). KUPFFER, CARL VON. Studien sur vergleichende Entwick- lungsgeschichte des Kopfes der Kranioten 1. Die Entwicklung des Kopfes von Acipenser sturio an Medianschnitten untersucht. pp. 95. Nine plates. Seven figures in text. Jfiinchen and Leipsig, 1893. Important contribution to the delimitation of the wall of the brain. On page 84 is a reconstruction of head-cavities of Am- moceetes (see Fig. 72). Figs. 21 and 22 in the plates repre- sent cerebral vesicle of Amphioxus. (Cf. Fig. 51.) LANKESTER, E. Ray, and WILLEY, A. The Development of the Atrial Chamber of Amphioxus. Quarterly Jour. Micro. Sc. XXXI. 1890. pp. 445-466. Four plates. 87 88 89 go gi g2 93 REFERENCES. 305 LEUCKART, RUDOLPH, und PAGENSTECHER, ALEX. Unter- suchungen iiber niedere Seethiere. Amphioxus lanceolatus. Miiller’s Archiv f. Anat. u. Physiol. 1858. pp. 558-569. Taf. XVIII. Description of larvae of Amphioxus taken off Heligoland. Drew attention to larval asymmetry, and to the existence of the brain-ventricle (cerebral vesicle). In absence of knowledge of early development their interpretation of many of the structures (especially praoral pit, mouth, and_ gill-slits) was incorrect. Latter applies also to Schultze’s observations. Lworr, Basttius. Uber Bau und Entwicklung der Chorda von Amphioxus. Mittheilungen a. d. Zool. Station. Neapel. 1X. 1891. pp. 483-502. One plate. Consult this memoir for previous literature on histology of notochord. Lworr, BasiLtus. Ueber einige wichtige Punkte in der Ent- wicklung des Amphioxus. Biologisches Centralblatt, XI]. 1892. pp- 729-744. Eight figures. Notes absence of mesodermal “ pole-cells.” From frequency of mitoses in dorsal ectoderm of gastrula, concludes that the material destined to form dorsal wall of archenteron, from which notochord and myoccelomic pouches arise, grows in from the ectoderm round dorsal lip of blastopore. Hence notochord and mesoderm are essentially derived from ectoderm! MARSHALL, A. MILNES. Vertebrate Lmbryology. London, 1893. Muxuer, Jouannes. Uber die Fugendzustinde einiger See- thtere. _Monatsbericht der k6nigl. preuss. Akad. der Wissen- schaften zu Berlin. 1851. pp. 468-474. First accurate description of larva of Amphioxus, p. 474. In 1847 Johannes Miiller obtained a young Amphioxus of 2} mm. at Helsingfors. He says that the appearance of the gill-slits was peculiar, in that there were two rows of slits in the pharyngeal wall, placed one above the other. In the upper row were /ve round slits, while the lower slits were vertically elongated and were fourteen in number. He adds that it was doubtful whether it represented the young “ Branchiostoma lubricum ” or belonged to a new species. Mucer, WitnELM. Ueber die Hypobranchialrinne der Tunt- katen und deren Vorhandensein bet Amphioxus und den Cyklo- stomen. Jenaische Zeitschrift f. Naturwiss. VII. 1873. pp. 327-332. Piatt, Junta B. /urther Contribution to the Morphology of the Vertebrate Head. Anat. Anz. VI. 1891. pp. 251-265. 95 96 97 99 100 Iol 103 REFERENCES. Rasy, Carr. Uber die Differensierung des Mesoderms. Anat. Anz. III. 1888. pp. 667-673. Eight figures. Discovery of the sclerotome-diverticulum in embryo of Pristiurus. Ricr, HENry J. Observations upon the Habits, Structure, and Development of Amphioxus lanceolatus. American Nat. XIV. 1880. pp. 171-210. Plates 14 and 15. Author was the first to find Amphioxus in Chesapeake Bay. With regard to development, he gives some fairly good figures of larvee, and observed some of the more obvious features of the metamorphosis, as already described by Kowalevsky. RUCKERT, JOHANNES. Ueber der Entstehung der Lexcretions- organe bet Selachiern. Arch. fiir Anat. u. Physiol. (Anatomische Abtheilung). 1888. pp. 205-278. Three plates. Contains also the discovery of segmental origin of gonads. SCHNEIDER, ANTON. Seitrdge sur vergleichenden Anatomie und Entwicklunesseschichte der Wrrbelthiere, /1. Anatomie und Lntwickl. von Petromyszon und Ammocates. 4°. Ten plates. Berlin, 1879. Figure of the ciliated grooves in pharynx of Ammoceetes, at page 84. SCHULTZE, MAx. Beobachtung junger Lexemplare von Ampht- oxus. Zeit. f. Wiss. Zool. II. 1851-2. pp. 416-419. Two larve from Heligoland. Good description of structure of notochord. vAN Winn, J. W. Ueber Amphiovus. Anat. Anz. VIII. 1893. pp. 152-172. Witiey, A. Ox the Development of the Atrial Chamber of Amphioxus. (Preliminary communication.) Proceedings of the Royal Society, XLVIII. 1890. pp. 80-89. Witiey, A. The Later Larval Development of Amphioxus. Quarterly Jour. Micro. Sc. XXXII. 1891. pp. 183-234. Three plates. WILSON, EpMuND B. On Afidtiple and Partial Devolopment in Amphioxus. Anat. Anz. VII. 1892. pp. 732-740. Eleven figures. In this and the following more detailed paper, the author describes and interprets a remarkable series of experiments on the artificial production of twins and dwarfs. Besides this, there are many important observations on the normal cleavage of the egg. WILson, EDMUND B. Amphiovus and the Mosaic Theory of Development. Journal of Morphology, VIII. 1893. pp. 579- 638. Ten plates. 104 REFERENCES. 307 ZIEGLER, H. Ernst. Der Ursprung der mesenchymatischen Gewebe bez den Selachiern. Archiv f. Mikr. Anat. XXXII. 1888. pp. 378-400. One plate. Independent discovery of sclerotome-diverticulum. (See Rabl.) IV. ASCIDIANS. For bibliography relating to the Ascidians, see Professor W. A. HERD- MAN’S Reports on the Tunicata collected during the ‘‘ Challenger ” expedition — Parts J.-III. 1882-88; and also KORSCHELT und HEIDER, “Lerhbuch der vergleichenden Entwicklungsgeschichte der wirbellosen Thiere.” Heft III. Jena, 1893. 105 106 107 108 109 IIo V. PROTOCHORDATES, ETC. AYERS, HowarbD. Concerning Vertebrate Cephalogenesis. Jour. Morph. IV. 1890-91. pp. 221-245. BATESON, WILLIAM. JAZemoirs on the Development of Balano- glossus. Quarterly Jour. Micro. Sc. Vols. XXIV.-XXVI. 1884-86. Brooks, W. K. The Systematic Affinity of Salpa in tts Relation to the Conditions of Primitive Pelagic Life ; the Phylogeny of the Tunicata ; and the Ancestry of the Chordata. Part II. of Monograph of the Genus Salpa. Johns Hopkins University. Baltimore, 1893. BURCKHARDT, RuDOLF. Die Homologieen des Zwischenhirn- daches und thre Bedeutung fiir die Morphologie des Hirns bet niederen Vertebraten. Anat. Anz. IX. 1894. pp. 152-155 and 320-324. Relates to neuropore of craniate Vertebrates. Author calls the lobus olfactorius impar of Kupffer, the vecessus neuroporicus. CLAPP, CORNELIA M. Some Points in the Development of the Toadjish (Batrachus Tau). Jour. Morph. V. 1891. pp. 494- pol. Observations on the double origin of mouth, made in 1889, not published in this paper. DaviporF, M. von. Ueber den “Canalis neurentericus antertor bei den Asctdien.” Anat. Anz. VIII. 1893. pp. 301-303. 308 REFERENCES. III Dourn, ANTON. Studien zur Urgeschichte des Woarbelthier- korpers, I. Der Mund der Knochenfische. Mitth. Zool. Stat. Neapel. III. 1881-2. pp. 253-263. 112 FIELD, GEoRGE W. The Larva of Asterias vulgaris. Quarterly Jour. Micro. Sc. XXXIV. 1892. pp. 105-128. 113 Fow er, G. HERBERT. The Morphology of khabdopleura Normant Allman. Festschrift fiir Rudolf Leuckart. pp. 293-297. Leipzig, 1892. 114 HarM_Er, S. F. See M’INTOSH. 115 HERDMAN, W. A. Article ‘‘ Tunicata.” Ency. Brit. 9th ed., republished in “ Zodlogical Articles ” by Lankester, etc. 116 Huprecut, A. A. W. Article “ Nemertines... Ency. Brit. oth ed., republished in “ Zodlogical Articles” by Lankester, etc. 116 ézs. HUBRECHT, A. A. W. On the Ancestral Form of the Chordata. Quarterly Jour. Micro. Sc. XXIII. 1883. pp. 349-368. For later works on this subject see Notes to Chap. V. 117 KUPFFER, C. VON. Lutwickelungsgeschichte des Kopfes. In Merkeland Bonnet’s Ergebnisse der Anatomie und Entwickelungs- geschichte, II]. 1893. pp. 501-564. 118 LANG, ARNOLD. Zum Verstandnis der Organisation von Cephalodiscus dodecalophus M’Int. Jenaische Zeitschrift f. Naturwiss. XXV. 1891. 119 LANG, ARNOLD. Ueber den Einfiuss der festsitzenden Lebens- weise auf die Thiere. Jena, 1888. 120 LANKESTER, E. Ray. Degeneration: a Chapter in Darwinism. Nature Series. London, 1880. Republished in “ The Advance- ment of Science; Occasional Essays and Addresses.” London, 1890. : 121 LANKESTER, E. Ray. A Contribution to the Knowledge of Rhabdopleura. Quarterly Jour. Micro. Sc. XXIV. 1884. pp. 622-647. 122 MacBripe, E. W. Zhe Organogeny of Asterina Gibbosa. Proceedings Royal Society. Vol. 54. 1893. pp. 431-436. 123 M’INTOSH, WILLIAM C. Report on Cephalodiscus dodecalo- phus, M’Intosh. ‘* Challenger” Reports. Zodlogy,XX. 1887. With Appendix by S. F. HARMER. 124 MorGan, T.H. Zhe Growth and Metamorphosis of Tornaria. Jour. Morph. V. 1891. pp. 407-458. 125 MorGan, T. H. Zhe Development of Balanoglossus. Jour. Morph. IX. 1894. pp. 1-86. 126 PLATT, JULIA B. Hurther Contribution to the Morphology of the Vertebrate Head. Anat. Anz. VI. 1891. pp. 251-265. Describes the double origin of mouth in Batrachus. REFERENCES. 309 127 POLLARD, H. B. Odservations on the Development of the Head in Gobius capito. Quarterly Jour. Micro. Sc. XXXV. 1894. PP. 335-352- 127 ds. POLLARD, H. B. The “ Cirrhostomial” Origin of the Head in Vertebrates. Anat. Anz. 1X. 1894. pp. 349-359. 128 RABL-RUCKHARD, H. Der Lobus Olfactorius Impar der Selachier. Anat. Anz. VIII. 1893. pp. 728-731. 129 SEDGWICK, ADAM. The Original Function of the Canal of the Central Nervous System of Vertebrata. Studies from Morph. Lab. Cambridge, II. 1884. pp. 160-164. 130 SEDGWICK, ADAM. JVotes on Elasmobranch Development. Quarterly Jour. Micro. Sc. XXXIII. 1891-92. pp. 559-586. Contains important observations on the first appearance of the mouth, and its relation to the pituitary body. 131 SEELIGER, OSWALD.* Studien zur Entwicklungsgeschichte der Crinoiden. (Antedon rosacea.) TZoologische Jahrbiicher. Abth. f. Anat. VI. 1892. pp. 161-444. 132 VAN WIJHE, J. W. Ueber den vorderen Neuroporus und die phylogenetische Function des Canalis Neurentericus der Wirbel- thiere. Zool. Anz. VII. 1884. pp. 683-687. 133 WILLEY, A. Studies on the Protochordata, 1-I/[. Quarterly Jour. Micro. Sc. XXXIV.-XXXV._ 1893. Contain further bibliographical references. INDEX. Acipenser sturio, 102, 129, 287. Acrania, 17, 46. AGASSIZ, A., 250, 251, 256. ALLMAN, 262. Ammocetes, 163-170, 173, 178, 182, 186, 282. ANDREWS, 39, 41. Annelid theory, 5, 79, 82, 97, 176, 282, 290, 293. Annelids, excretory system of, 78-82, 99. giant fibres of, 97, 103. nervous system of, 95-97. segmentation of, 4. vascular system of, 55. Antedon rosacea, 256, 268-269, 271. Anus, 14, 25, 118, 131, 187. Aorta, dorsal, 49, 50, 53. Aperture, buccal, 182. cloacal, 182, 183, 210. Appendicularia, 180, 236-239, 241, 277. Archenteron, IIo. Artery, branchial, 47, 50, 98, 139. genital, 98. Ascidians, pelagic, 181, 236. sessile, 181. Asterias vulgaris, 254, 270. Asterina gibbosa, 270, 271. Asymmetron lucayanum, 40, 41. Asymmetry, 155-162, 177. Atriopore, 14, 77, 105. Atrium (see also Cavity, peribranchial), 14, 22, 186, 195. development of, 75-78, 210-212. post-atrioporal extension of, 25. Audition, 44. AUDOUIN, 197. Auricularia, 251-253, 256, 268. Axis (see Relations, axial). AYERS, 18, 173. Balancers, 42. Balanoglossus, 29, 43, 98, 128, 221, 222, 231, 242-253, 259, 261, 264, 265, 274, 276. Balanoglossus, nervous system of, 244- 246. Kowalevskit, 248, 250. ‘upfrert, 248, 253. BALFOUR, 5, 38, 79, 175, 190, 203, 273, 283, 292. Band, adoral ciliated, 250. circumoral ciliated, 251, 256. longitudinal ciliated, 251. post-oral (circular) ciliated, 251, 256. Bands, mesodermic, 120, 217, 218. peripharyngeal, 34, 140, 145, 168-169, 179, 185, 195, 226. Bars, branchial (see Gill-bars). BATESON, 98, 221, 244, 245, 250, 259, 263, 291. Batrachus tau, 281. Bdellostoma, 173, 285. BEARD, 208, 281, 292. BEDDARD, 81. VAN BENEDEN, 187, I9I, 197, 200, 224, 291. BENHAM, 33, 42. BERT, 174. Bipinnaria, 251. Blastoccel, 108, 254, 255. Blastomeres, 107. Blastopore, 110, 112, 197. Blastula, 108, 197. Blood-sinuses, I91, 192. Blood-vessels, contractile, 47, 98. origin of, 122. Bodies, polar, 106. Body, pineal, 207. pitituary (see Hypophysis). Body-cavity (see also Coelom), 217, 220- 222, 247. preeoral, 128, 218. Bojanus, organ of, 194. Botryllus, 181, 240. | BOULENGER, 14. BOURNE, A. G., 81. BOVERI, 42, 48, 60, 98, 99, 100, 151, 177. Brachiolarta, 270. 311 312 Brain, 92, Ior. Branchiomery, 65, 132. Branchiostoma cultellum, 40. lubricum, 8. Breeding-season, 105. Brood-pouch, 215. BROOKS, 254, 277, 289. Bulbils, vascular, 48. BURCKHARDT, 284. Bury, H., 269. CALDWELL, 291. Canal, alimentary, 24, 111, 187, 196, 214, 235, 249, 264. neurenteric, 114, 118, 199, 202, 275. Capillaries, 49, 98. Capitellida, 81. Cartilages, buccal, 18, 147. labial, 18. Caulus, 266. Cavity, opercular, 22. peribranchial (see also Atrium), 22, 183, 186, 195, 209. peritoneal, 22. Cells, epithelio-muscular, I91. Cellulose, 182. Cenogenesis, 177. Cephalisation, 75, 89. Cephalochorda, 13. Cephalodiscus, 261-267, 280, 289. Chetognatha, 278. Ciona intestinalis, 203, 210, 215, 222, 224, 226, 229, 230-235, 240, 271, 288, 292, 293. Cirri, buccal, 12, 20, 145. Cladoselachida@, 44. CLAPP, CORNELIA, 281. Clavelina, 181, 185, 187, 200, 215, 225, 241, 288. Cleavage, 107, 197. polymorphic, 108. Ceeca, intestinal, 249, 261. Caciliani, 67. Coecum, hepatic, 24, 236. Coelom, 22, 26, 31, 33, III, I2I, 122, 220- 222, 247-248, 265, 206. perigonadial, 153, 177. ‘Coencecium, 263. Collar-pores, 98, 248, 265. Collar-region, 242, 264. Collector, 45, 165. Commissure, circumoesophageal, 96, 273, 280, Compression, bilateral, 15, 43, 115. INDEX. Contraction, peristaltic, 98, 192. Cordon ganglionnaire viscéral, 224. COSTA, 7, Io. Craniota, 17. Crinoidea, 268. Cross-bars, 28. CUNNINGHAM, J. T., 80. Cutis, 38, 41, 122. CUVIER, 3. Cyclostomata, 8, 10, 45, 208. Cyclostome, 46. Cynthia papillosa, 200. DAVIDOFF, 200. DEAN, B., 44. Degeneration, 5. Development, abbreviated, 214, 215, 239. adolescent period of, 149, 150. direct, 250. duration of larval, 149, 169, 203, 215- embryonic, 114, 201. larval, 117, 130. latent, 145, 160. precocious, 161, 212. Differentiation, sexual, 154. Dissepiments (see Septa). Distaplia magnilarva, 206, 225, 288. Distribution, 11, 40-41. Diverticula, anterior intestinal (see also Head-cavities), 115. DOHRN, 5, 30, 167, 173, 176, 178, 179, 280, 281, 282. Duct, mesonephric, 66. pronephric, 69, 78, 99. Dura mater, 87. Echinoderms, 250-256, 267-271, 291. Ectoderm, 24, 78. ciliated, 112, 113, 130, 175, 243, 257. definitive, 111. primitive, 110. EISIG, 45, 81, 94, 103, 293. Embryo, ciliated, 113, 214. ventral curvature of Ascidian, 201. EMERY, 67. Endoderm, definitive, 111. primitive, 110. Endostyle, 9, 24, 31, 39, 130, 138, 149, 150, 167, 177, 185, 195, 227, 229, 250. Enteroccel, 252, 254, 255. LExnteropneusta, 242, Epiceele, 41. Epithelium, atrial, 33,59, 100, 209. coelomic, 33, 122, 220-222, INDEX. 313 Equilibration, 44, 205. Equilibrium, Io, 43. ERLANGER, 220. Evolution, parallel, 80, 247, 290. Eye of Ascidian tadpole, 102, 206. Eye, median, 18, 102, 130. myelonic, 207. pineal, 207-209. Eyes, paired, ro2. Fascia, 36, 123. FELIX, 99. Fertilisation, 106, 188. Fibres, giant, 92-94, 103. Miillerian, 94. of Mauthner, 94. supporting, 89. FIELD, G. W., 254. Fierasfer, 67. Fin, definitive caudal, 131. provisional caudal, 115. Fin-rays, 15. Fins, 15, 44. lateral, 38, 42. Fixation, organ of, 222, 229, 271, 280. FLEMMING, gg. Flexure, cranial, 92, 279. FOL, 239. Folds, medullary, 199. metapleural, 15, 38, 42, 43, 76, 132, 176. Follicle, tos. Food, 9, 39, 185, 249. FOWLER, G. H., 262, 266, 267. FRORIEP, 175. Function, change of, 176, 280. Funnels, atrio-ccelomic, 58, 98. brown (same as preceding). ceelomic (see also Nephrostomes), 62. FUSARI, 87, 163. Fusari, plexus of, 87, 178. FURBRINGER, 99. Ganglia, peripheral, 85, 88. spinal, 84, 103. Ganglion, Ascidian, 188, 224, 225. cerebral, 96, 270, 272-274. Ganglion-cells, 89, 91. bipolar, 95. giant, 92. multipolar, 92. GARSTANG, 240, 250. Gastrula, 110, 197. significance of, III. Gastrulation, Io9. GEGENBAUR, 249, 273. Germ-layers, primitive, 110, 114. Gill-bars, 28, 32-34. blood-vessels of, 48-49. Gill-pouches, 165, 166. Gill-slit, first, 117, 118, 132, 141, 166, 170— 172. Gill-slits (see also Stigmata), 17, 27, 100, 130-132, 135-138, 139, 148-149, 160, 173-174, 195, 229, 234, 243, 244, 264, 289. asymmetry of, 157-158. atrophy of, 140, 143, 149. Gland, club-shaped, 116, 117, 134, 138, I4I, 170-172, 176. Pyloric, 236. subneural, 188-191, 225. thyroid, 169-170. thymus, 29, 30. Glands, fixing, 204. Glomerulus, 64, 65, 69, 100. Gnathostome, 46. Gobius capito, 282. GoopsIR, 8. DE GRAAF, 208. Groove of Hatschek, 21, 51, 135. Groove, epibranchial, 226, hyperbranchial, 34, 39, 195. hyperpharyngeal (same as preceding). hypobranchial (see also Endostyle), 9, 167. medullary, 112, 198. pericoronal (see Bands, peripharyn- geal). peripharyngeal (see Bands, peripha- tyngeal). Gut, post-anal, 203, HAECKEL, 5, 46, III, 177. HANCOCK, Igo. HARMER, 263, 289. VAN HASSELT, 193. HATSCHEK, 4I, QI, 102, 103, 104, I12, IIS, 118,174, 175, 292. Hatschek’s nephridium, 172. Head-cavities of Ammoceetes, 129. of Amphioxus, 126-128. preemandibular, 128, 175, 279-280. of Sagitta, 277. Heart, 46, 51-53, I9I, 192. recurrent action of, 193. HEIDER (see KORSCHELT and HEIDER). Hleptanchus, 173. 314 HERDMAN, 183, 277, 293. Hermaphrodite, 187, 196. Hexanchus, 173. HJorT, 225, 293. HOCHSTETTER, 54. Hood, nerve-plexus of oral, 84, 178. oral, 12, 147, 150, 178. HUBRECHT, 258, 259, 260, 287, 291. HUXLEY, 20, 22, 41, III. Hypophysis, 160, 165, 178, Ig0, Ig1, 195, 225, 283-288, 290, 292. Ichthyophis glutinosus, 67. Infundibulum, 102, 283, 285. dnsects, compared with Vertebrates, 2-4. Involutions, atrial, 209, 241. JULIN, 187, 190, 197, 200, 224, 225, 226, 292. KASTSCHENKO, 175. Kidney, 65. KLINCKOWSTROM, 207. KGlliker's olfactory pit, 19. KOPPEN, 103. KORSCHELT and HEIDER, 178. KOWALEVSKY, 4, 104, 114, 174, 196, 216, 240. KROHN, 197, 250. KUPFFER, I0I, 102, 128, 129, 175, 283, 287. Lamella, post-oral, 264. Lamina, dorsal, 183, 185, 195, 226. terminalis, 284. Lamprey (see Petromyzon). LANG, 291. LANGERHANS, 21, 56, 98, IOI, 154. Lanice conchilega, 80. LANKESTER, 38, 41, 58, 62, 98, III, 237, 262, 266. LEUCKART, Ioo. LEYDIG, 4. Ligamentum denticulatum, 25, 63, 164. Limax lanceolatus, 7. Line, lateral, 21, 42-45. Liver, 24. Lobe, przeoral, 218, 222, 228, 229, 254, 267-280, 290, 292. procephalic, 272. Lobus olfactorius impar, 102, 283, 284. Locomotion, caudal, 103, 203. ciliary, 121. muscular, 121. Loimia medusa, 80. INDEX. Lumbricus, 79, 272. LWOFF, 175. Lymph-spaces, 15, 51. MACBRIDE, 271. Mantle, cellulose, 183. muscular, 183. MARSHALL, MILNES, 177. Maturation, 106. Mauthner, fibres of, 94. MAYER, PAUL, 99, I00. Medulla oblongata, gr. Membrane, interccelic, 152. vitelline, 105. Merlucius, 67. Mesenchyme, 201, 217, 220-222, 261. Mesoderm, III, II4, 120, 122, 199-201, 221. Mesonephros, 66. Metamerism, 64, 132, 196, 246-247, 291. Metamorphosis, 136, 150, 215, 223, 250, 256. Metanephros, 66. METCALF, 293. METSCHNIKOFF, 251. MEYER, EDUARD, 80. MILNE-EDWARDS, 197. MINOT, I55. M'INTOSH, 263. Molgula, 194. Molgula manhattensis, 210, 232, 240. Moroav\, T. H., 232, 245, 247, 253, 256, 274. Mouth, 19, 117, 131, 143-144, 146, 150, 176, 178, 229, 276, 280-282. asymmetry of, 157-160. MULLER, FRITZ, 250. MULLER, J., 8, 18, 50, 56, 59, 250. MULLER, W., Io2, 167. Muscles, 34-37, 86, 122, 195, 203, 222, 235. Muscle-fibres, origin of, r2r. Musculature (see Muscles). Myoccel, 121. Myotomes, 13, I50. Myxine, gill-slits of, 171. hypophysis of, 285. pronephric duct of, too. NANSEN, 103. NASSONOFF, Igo. Nemertines, 249, 256-261, 272, 273. lateral nerves of, 259. medullary nerve of, 259, 260. Nephridium, 62, 79, 99, 261. INDEX. Nephrostomes, 65, 69, 72. Nerve-cord, ventral, 96, 259, 273, 289. Nerves, cranial, 85. motor, 86, 100. R. branchialis vagi, 163, 164. Rr. cutanei ventrales, 44. R. recurrens trigemini et facialis, 45. R. cutaneus quinti (same as preced- ing). R. lateralis trigemini (same as pre- ceding). R. dorsalis, 85, 103. R. lateralis vagi, 45, 259. R. ventralis, 85, 103. R. visceralis, 86. sensory, 86, spinal, 83. Nerve-tube (see Tube, medullary). Nervous system, origin of central, 111, I1g, 198. Neuropore, I9, 90, I15, 160, 199, 202, 223, 225, 283, 285, 287, 292. NORMAN, CANON, 262. Notidanide, 173. Notochord, 8, 13, III, 115, 124-126, 158, 161-162, 199, 216, 222, 244, 266, 286, 287, 290. Ontogeny, 177. Operculum, 264. Organs, renal, 55, 194. reproductive (see also Pouches, gonadic), 122, 151-155, 187-188, 246, 266. Otocyst, 205. Otolith, 10, 205, 224. Oviduct, 187. Ovum, 105. OWSJANNIKOW, Ioo. PAGENSTECHER, 100. Palingenesis, 177. PALLAS, 7. Paludina vivipara, 220. Papillze, adhesive, 204. renal, 56-57, 59. Pericardium, 191, 218. Pericheta, 81. Petromyzon, 93, 163, 169, 286. Phallusia, 203, 232, 292. Pharynx, 27, 183. Phylogeny, 177. Pigment, 18, 26, 33, 102, 130, 131, 134, 204. 315 Pigment-cells, 135. Pilidium, 272. Pit, olfactory, 19, 90, 145, 160, 165, I95, 283, 285, 292. preeoral, 51, 128, 135, 144, 148, 267. Plate, apical, 255-256, 269, 270, 272-274, 292. medullary, 113, 115, 118, 198. Plates, skeletal (endostylar), 32. PLATT, JULIA, 175. ‘ Pleuronectid@, 3, 40, 162, 178. Plexus, branchial, 163, 164, 165. Pluteus, 268, 270. | Pole-cells, mesoblastic, 175. POLLARD, H. B., 282. Pontobdella, 81. Porus branchialis, 23. Pouches, archenteric, 114, 115, 120, 247, 248. gonadic, 13, 25, 40, 153-154. myoccelomic, 122. POUCHET, 82. Pristiurus, 99. Proboscis, 221, 242, 247, 257, 264. Proboscis-cavity, 247. Proboscis-pore, 128, 248, 253, 264. Proboscis-sheath, 258. Products, genital, 174. Pronephros, 66-75, 78. blood-vessels of, 63, 69, 74, 100. development of, 69, 78. Prostomium, 272. Protopterus, 14. Pyrosoma, 181, 236, 241. QUATREFAGES, 88, 174. RABL, 175. RABL-RUCKHARD, 284. Raderorgan, 21, 148. RATHKE, 8. Recessus opticus, 102. Rectus abdominis, 35. Relations, axial, 226-229. RETZIUS, 82, 100, 103. Rhabdopleura, 261, 262, 266, 267. Ridge, epibranchial, 226. Ridges, subatrial, 76. RITTER, 250. Rods, skeletal, 28. ROHDE, 100, I0I, 103. ROHON, 82, 86, 163, 165. ROLPH, 23, 41, 56, 86, 98. RUCKERT, 60, 99, 100, 154. 316 Sac, branchial (see also Pharynx), 183, 195, 227. Sagitta, 13, 277-278. SAINT-HILAIRE, I, 279. principles of, 2, 279. SALENSKY, 206. Salpa, 180, 182, 193, 236, 241. Sarcolemma, 36. SARs, G. O., 262. SAVIGNY, Igo. Schizoceel, 175. SCHMIDT, KARL, 182. SCHNEIDER, ANTON, 35, 38, 98, 100, 178. Sclerotome, 123, 175, 221. SEDGWICK, ADAM, I12, 289, 291. SEELIGER, 239-240, 269, 277. Segmentation (see Cleavage). Segmentation-cavity, 108. SEMON, 67. SEMPER, 5, 79, 99, 176. Sense-cells, 20, 21. Sense-organ of przoral pit (see Groove of Hatschek). Septa, 13, 37, 122. Sheath, notochordal, 38, 123. SHELDON, LILIAN, 293. Shield, buccal, 263. Skeleton, axial, 13. Snout, 115, 218. Somites, mesodermic, 115, 121. Spawning, Ios. Species of Amphioxus, 41. SPEE, GRAF, 99. SPENCER, BALDWIN, 207, 208, 209. SPENGEL, 38, 41, 248. Spermatozoa, 105. Spinal cord, 83, 222. central canal of, 89, 289. Spiracle, 173. Spiraculum, 23. Splanchnoceel, 122. Stage, critical, 149, 174. STANNIUS, 45. STIEDA, Ioo. Stigmata, 183, 195, 196, 227. formation of, 229-235. Stomodceum, 165, 209. Sympathetic system, 35, 86. Synapticula (see Cross-bars). Table, showing order of development of Ascidian and Amphioxus, 213. INDEX. | Tadpole, Batrachian, 14. | Tail of Ascidian tadpole, 201-204, 212, 222. Teleosteans, 45, 281. Tentacles, velar, 20, 195. Test, 182, 240. THACHER, 38. Thymus, 29. Tissue, connective, 37, 41, 122. mesenchymatous, 221. Tongue-bars, 28, 140, 142, 148, 231. Tornaria, 250-253, 255-256, 270, 274. Trochophore, 256, 272. Tube, medullary, 114, 120, 198, 274. neuro-hypophysial, 225. Tubercle, dorsal, 189, 225. Tuberculum posterius, Io2. Tubules, excretory, 59-65, 72, 100, I22. mesonephric, 70, 177. pronephric, 67, 70, 78, 100. uriniferous, 65. Tunic (see Test). Ureter, 66. Urmund, Ito. Ussow, Igo. Vacuolisation of notochord, 125, 216, 240, 244. Vas deferens, 187, Vein, cardinal, 54. caudal, 54. hepatic, 49, 98. portal, 53, 98. sub-intestinal, 49, 53-55. Velum, 20, 50, 150, 178. Vesicle, cerebral, 90, 100, 204, 223, 224, 226. Water-pore, 253, 254. WEISS, F. E., 57, 59. VAN WIJHE, 39, 50, 51, 88,99, 128, 163, 164, 165, 178, 280. WILDER, BuRT G.,, 14. WILSON, E. B., 108, 174, 175, 292. WoOoDWARD, A. S., 44. YARRELL, 8. | ZIEGLER, H. E,, 175. | Zoarces, 67. Columbia University Biological Series. EDITED BY HENRY FAIRFIELD OSBORN, Da Costa Professor of Biology in Columbia College. This series is founded upon a course of popular University lectures given during the winter of 1892-3, in connection with the opening of the new department of Biology in Columbia College. The lectures are in a measure consecutive in charac- ter, illustrating phases in the discovery and application of the theory of Evolution. Thus the first course outlined the de- velopment of the Descent theory; the second, the application of this theory to the problem of the ancestry of the Vertebrates, largely based upon embryological data; the third, the applica- tion of the Descent theory to the interpretation of the structure and phylogeny of the Fishes or lowest Vertebrates, chiefly based upon comparative anatomy ; the fourth, upon the problems of individual development and Inheritance, chiefly based upon the structure and functions of the cell. Since their original delivery the lectures have been carefully rewritten and illustrated so as to adapt them to the use of Col- lege and University students and of general readers. The vol- umes as at present arranged for include: I. From the Greeks to Darwin. By Henry Farrrieip OSBORN. II. Amphioxus and the Ancestry of the Vertebrates. By ArtHur WILLEY. III. Fishes, Living and Fossil. By Basnrorp Dean. IV. The Cell in Development and Inheritance. By Epuunp B. WILson. Two other volumes are in preparation. MACMILLAN & CO., 66 FIFTH AVENUE, NEW YORK. J. FROM THE GREEKS TO DARWIN. THE DEVELOPMENT OF THE EVOLUTION IDEA. BY HENRY FAIRFIELD OSBORN, Sc.D, PRINCETON, Da Costa Professor of Biology in Columbia College. Ready in September. This opening volume, “ From the Greeks to Darwin,” is an outline of the development from the earliest times of the idea of the origin of life by evolution. It brings together in a continu- ous treatment the progress of this idea from the Greek philoso- pher Thales (640 3B.c.) to Darwin and Wallace. It is based partly upon critical studies of the original authorities, partly upon the studies of Zeller, Perrier, Quatrefages, Martin, and other writers less known to English readers. This history differs from the outlines which have been pre- viously published, in attempting to establish a complete conti- nuity of thought in the growth of the various elements in the Evolution idea, and especially in the more critical and exact study of the pre-Darwinian writers, such as Buffon, Goethe, Erasmus Darwin, Treviranus, Lamarck, and St. Hilaire, about whose actual share in the establishment of the Evolution theory vague ideas are still current. TABLE OF CONTENTS. I. THE ANTICIPATION AND INTERPRETATION OF NATURE. II. Aone THE GREEKS. III. THE THEOLOGIANS AND NATURAL PHILOSOPHERS. IV. THe EvoLurionists oF THE EIGHTEENTH CENTURY. V. From LamMarck To St. HILAIRE. VI. Tue First HALF-cENTURY AND DARWIN. In the opening chapter the elements and environment of the Evolution idea are discussed, and in the second chapter the re- markable parallelism between the growth of this idea in Greece and in modern times is pointed out. In the succeeding chap- ters the various periods of European thought on the subject are covered, concluding with the first half of the present century, especially with the development of the Evolution idea in the mind of Darwin. Il. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES. BY ARTHUR WILLEY, B.Sc. LONo., Tutor in Biology, Columbia College ; Balfour Student of the University of Cambridge. Ready in September. The purpose of this volume is to consider the problem of the ancestry of the Vertebrates from the standpoint of the anat- omy and development of Amphioxus and other members of the group Protochordata. The work opens with an Introduction, in which is given a brief historical sketch of the speculations of the celebrated anatomists and embryologists, from Etienne Geoffroy St. Hilaire down to our own day, upon this problem. The remainder of the first and the whole of the second chapter is devoted to a detailed account of the anatomy of Amphioxus as compared with that of higher Vertebrates. The third chapter deals with the embryonic and larval development of Amphioxus, while the fourth deals more briefly with the anatomy, embryology, and relationships of the Ascidians; then the other allied forms, Balanoglossus, Cephalodiscus, are described. The work concludes with a series of discussions touch- ing the problem proposed in the Introduction, in which it is attempted to define certain general principles of Evolution by which the descent of the Vertebrates from Invertebrate ancestors may be supposed to have taken place. The work contains an extensive bibliography, full notes, and 135 illustrations. TABLE OF CONTENTS. INTRODUCTION. CHaprer I. ANATOMY OF AMPHIOXUS. II. Ditto. III]. DevELOPMENT OF AMPHIOXUS. IV. Tue ASCIDIANS. V. THE PROTOCHORDATA IN THEIR RELATION TO THE PROBLEM OF VERTEBRATE DESCENT. III. FISHES, LIVING AND FOSSIL. AN INTRODUCTORY STUDY. BASHFORD DEAN, PH.D. COLUMBIA, Instructor in Biology, Columbia College. This work has been prepared to meet the needs of the gen- eral student for a concise knowledge of the Fishes. It contains a review of the four larger groups of the strictly fishlike forms, Sharks, Chimaeroids, Teleostomes, and the Dipnoauns, and adds to this a chapter on the Lampreys. It presents in figures the prominent members, living and fossil, of each group; illustrates characteristic structures; adds notes upon the important phases of development, and formulates the views of investigators as to relationships and descent. The recent contributions to the knowledge of extinct Fishes are taken into special account in the treatment of the entire subject, and restorations have been attempted, as of Dinichthys, Ctenodus, and Cladoselache. The writer has also indicated diagrammatically, as far as generally accepted, the genetic relationships of fossil and living forms. The aim of the book has been mainly to furnish the student with a well-marked ground-plan of Ichthyology, to enable him to better understand special works, such as those of Smith Wood- ward and Giinther. The work is fully illustrated, mainly from the writer’s original pen-drawings. TABLE OF CONTENTS. CHAPTER “ 2 I. Fisoes. Their Essential Characters. Sharks, Chimaeroids, Teleo- stomes, and Lung-tishes. Their Appearance in Time and their Distribution. II. Tut Lampreys. Their Position with Reference to Fishes. Bdel- lostoma, Myxine, Petromyzon, Palaeospondylus. III. Tue SHark Group. Anatomical Characters. Its Extinct Members, Acanthodian, Cladoselachid, Xenacanthid, Cestracionts. 1V. Coimazroips. Structures of Callorhyuchus and Chimaera. Squalo- yaja and Myriacanthus. Life-habits and Probable Relationships. V. Teteostomes. The Forms of Recent ‘‘Ganoids.” Habits and Dis- tribution. The Relations of Prominent Extinct Forms. Crosso- pterygians. Typical ‘‘ Bony Fishes.” VI. Tue Evonvution or THE Groups oF Fisnes. Aquatic Metamerism. Numerical Lines. Evolution of Gill-cleft Characters, Paired and Unpaired Fins, Aquatic Sense-organs. VIL. Tue DEVELOPMENT oF FisHEs. Prominent Features in Embryonic and Larval Development of Members of each Group. Summaries. at (ts Poteess Sethe aM Howe eri EY fe! ef uhh PRE DE hb lial en tat nes Sica LEM Ath a3 a eee ee " Ved ry ry a} bhistelarst Salstate it} ® * “a gz arate Tete ne ti a : aaa tet seenets ih gas Tat ah ay LIN). i + r a : Ab} > Ft, * sit 23, ‘DF et) , ened! aa Bt i Rat Ha teeat rt x te 5 %. 8, % * LIEN St . in ars ° Le See ats 1a o8 * ee There as iweb oh Selescl ays . aK * AM iiss ste Mb atta Pha ¢ * altace TAR Be atyea tals t sie: Rist eent ee, me a sewn ay oor ey, ij