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With 6 Copper plates. CHRISTIANIA. PRINTED BY BROGGER & CHRISTIE. "1 872. Bee Wald | eh aa fo aN ee re LB 7 Bere ay ,, ‘ae oV S08 Rin. fs ; ue ust agua ye | TL. meRoeNIO'. an 0; Baer 9 e = a 2 ‘ . . : : *, va : . \ 7, ae ! u ‘ { * a a 3 7 4 = 4 4 J -¥ - : . eee ) § = , Pp 4 A ans, weak. : } \ . NG WEA ANIC sO LAC AA & «ronnie tan) dni H we ‘ < Pa iy é, PSLER: At joy Pe i > it bs A wf: j 7 _ “iis © al : : Stee V7; yi? 7 = j ed -. * a a pate ‘ - [eee peel i i ; mat Seto tis | : ? 4 Fa i Py 1 5 ie) ‘ait CVA ss ; daar hl ey a * Preface Introduction i 10. VE Polyzoa. Rhabdopleura mirabilis The Polyparium The Polypide The tentacular arms The bucal shield The contractile cord The axial cord . Vital phenomena Occurrence Characteristics of genus and species . Development . Concluding remarks Flustra abyssicola Conchifera. Yoldia obtusa Pecchiolia abyssicola Cephalophora. Dentalium agile Triopa incisa . Goniéolis typica . Annelida. Umbellisyllis fasciata Paramphinome pulchella Anthozoa. Mopsea borealis . Fungiacyathus fragilis Contents, ih pag. — nnwenes © DH & & i er ow - w IV Spongie. 12. Trichostemma hemisphericum 13. Cladorhiza abyssicola 14. Hyalonema longissimum Explanation of the plates 62 65 70 74 . Preface. Under the above title I purpose, if I can obtain the necessary assistance, to make known little by little the most important discoveries which I have had opportunity to make during my deep-sea. investigations in recent years; and I.shall consider it my duty first to treat those animal forms which my Father has already partially examined and designated. The present university-program comprises some of these belonging to 6 different classes of animals, namely 2 Polyzoa, 2 Conchifera, 3 Cephalophores, 2 Annelids, 2 Corals and 3 Sponges. These animal forms had already been partially destined by my Father for more detailed notice in a university-program similar to that composed on the subject of the Rhizocrinus; and application for the requisite assistance was already sent in to the academical college, when his unexpected death put a sudden end to the important investigations which he had commenced. ; It is therefore with deep gratitude that I here acknowledge the kindness of the col- lege, in confiding to me the elaboration and publishing of the intended program; and although I am well aware of my want of that thorough acquaintance with the invertebrate animals, and _ of that clear and precise method of treatment which always distinguished my Father’s works, it is still a pleasure for me to have opportunity given for prosecuting to the best of my power those investigations, to which my Father devoted himself with so much zeal and perseverance, until the day of his death. Although, as above stated, the present program was intended to be published by my Father, still the necessary detailed investigations were scarcely more than commenced, for which reason also no manuscript had been compiled. I find however, among my late Father’s papers, notes on most of the animal forms mentioned in the following lines, and with respect to some of them also more complete descriptions, which have been of great help to me in the elaboration of the present program. I have also always quoted as conscienciously as possible my Fathers’s more coherent remarks, which certainly will have their important value. Where this has taken place, I have always expressly remarked it in the text. Finally I am bound to express my warmest thanks for the valuable information relative to the Mollusca, which has been communicated to me by the celebrated English Conchologist I. Gwyn Jeffreys Esq.; and for the remarkable kindness with which the equally highly celebrated Swedish \Al Zoologist Professor S. Loven has sent me specimens of deep-sea sponges, for comparison with those discovered by me. With regard to the composition in its entirety, I must represent myself as alone re- sponsible; so that the possible defects noticeable in this respect may be attributed to me and not to my Father. That I have chosen a foreign language, instead of my mother tongue as the medium of this communication, is a circumstance which I think does not call for any justification on my part. Science is cosmopolitan, and therefore requires a generally intelligible language. Our language has not reached this point yet; and to facilitate the reading of this little work, I have adopted one of the great universal languages. I have preferred the English language, as well because it has most affinity with our own, and consequently affords greater facility for rendeting the Norwegian expressions, as in acknowledgment of the great progress which zoological science has made in recent times, through the medium of the English language. G. 0. SARS. Introduction. A wide field for zoological research, which has given, and will surely continue to give results of the highest scientific interest, has been lately opened by the investigation of the great depths of the sea, which had formerly been generally considered as void ofall life, but which have been found in some places to contain a wonderfully rich and varied animal world. Such deep-sea investigations have indeed been occasionally made at various points of our coast; and my Father gave already in 1864! a catalogue of 92 different forms of animal life, which were discovered by him and by other Norwegian naturalists, at the great depth of 200 —300 fathoms; and he had likewise previously — as early as 1850° — decidedly declared himself opposed to the hypothesis set forth by Forbes, and subsequently generally adopted, that the limit for the propagation of animal life in the depths of the sea should be fixed at about 300 fathoms. It is however only quite recently that such deep sea investigations have been conducted in a systematic manner on our coast. I had myself a particularly convenient opportunity for such research during my stay in Lofoten, where depths of 300 fathoms and more occur at a relatively small distance from land. I therefore determined, notwithstanding the great difficulties connected with dredging at such great depths, and although I had only ' an ordinary fishing-boat with a crew of 3 men at my disposal — to devote as much time as I could to these investigations, abandoning the far easier, and as I then thought far more productive, investigation of the smaller depths. The result of these my deep-sea researches was however, great and interesting quite beyond all anticipation. I found to my great sur- prise at this enormous depth -— not, as might be presumed according to Forbes’ hypothesis — a poor and oppressed Fauna, but on the contrary a richly developed and varied animal life; so that my Father was able in 1868*% to increase the catalogue of the forms of animal life observed at the depths of 200—8300 fathoms, by the addition of not less than 335 species — (in all 427) of which nearly all were taken in one locality, namely at the fishing-place Skraa- ven in-Lofoten. And so far was I from observing any sign of diminished intensity in this animal life at increased depths, that it seemed, on the contrary, as if there was just beginning 1 ,Bemerkninger over det dyriske Livs Udbredning i Havets Dybder.“ Christiania Videnskabs-Selskabs Forhand- linger for 1864. 2 Reise i Lofoten og Finmarken.* > ,Fortsatte Bemerkninger over det dyriske Livs Udbredning i Havets Dybder“. Chr. Vid.-Selsk. Forh. f. 1868. Vul to appear a rich and in many respects peculiar deep sea Fauna, of which only a very incom- plete notion had previously existed. The number of new forms of animal life was therefore also very considerable; and some of these were of peculiar interest, as more or less evidently carrying us back to former telluric periods, especially the Fauna of the Cretaceous period. This was specially evident in the case of an animal which my Father has therefore made the subject of a separate and detailed treatise. I mean the little remarkable sea-lilly Rhizocrinus lofotensis belonging to the family of the Apiocrinide, which has been considered as long ago extinct, but which flourished in the Oolitic period. The discovery excited great interest in the scientific world, and may be said to have given the impulse to the comprehensive investi- gations of the Atlantic depths, which have been instituted with great liberality by the English . government in later years. By these grand English deep-sea expeditions, in connexion with the deep-soundings executed during the Swedish Spitzbergen expeditions in the Arctic Ocean, which have both extended even to the enormous depth of between 2000 and 3000 fathoms, it has now been further ascertained that the great depths of the Ocean do not form, as was formerly supposed barren tracts or deserts, but are peopled with a richly developed and pe- culiar animal world, which on the whole shews a very clearly marked affinity to the Fauna of the Cretaceous period, and in a great measure may really be considered as consisting of descen- dents in direct line from the forms existing in that telluric period. This cannot indeed be always so evidently proved, as in the case of the above mentioned sea-lilly, but it is also in many other forms very distinctly expressed. We may therefore with Carpenter‘ presume that the Cretaceous formation is continued undisturbed at this present day in the depths of the Ocean; and we may therefore assume that just here, there has been little change during all the pe- riods of the earth; and we may also expect to find just here, the descendents from the chalk period most unchanged; while the Fauna at smaller depths, and especially the shore-Fauna, would in a relatively short time, by reason of telluric and physical revolutions, be forced entirely to change its character. It is also very probable that many of the remarkable forms of animal life, from the great depths off our coast, more particularly described in the follow- ing lines, are just such ancient slightly altered forms, which thus — apart from purely zoological considerations — excite’ a very peculiar interest, as giving us important indications with respect to the historical, or rather the paleontological development of animal life. ' See Carpenter on this subject. Preliminary report of dredging operations in the seas to the North of the British islands. p. 192. Polhly2oa. I. Rhabdopleura mirabilis. QM. Sars). Halilophus mirabilis. M. Sars. ,,Fortsatte Bemerkninger om det dyriske Livs Udbredning i Havets Dybder* p. 12. In the year 1866 I drew up in the dredge, together with other deep-sea animals, from a depth of 120 fathoms at Skraaven in Lofoten, a small ,,Phytozoon* to which at first I paid no great attention, as I took it to be a colony of Hydroids; I took therefore only afew exem- plars, and put them in spirit with some other uncertain forms of animal life from the same depth. After my return ‘home however, on examining more closely this supposed Hydroid colony, my Father found immediately that we had before us a very peculiar animal, which quite certainly could not be a Hydroid, but seemed rather to be related to the Polyzoa; although the shape and appearance of the single cells had undeniably a great resemblance to the former, especially to some Campanularides. As a satisfactory examination of the animal could not be made with the specimens brought home in spirit, my Father urged me, the next time I visited Lofoten to examine the animal in a living state as minutely as possible: as hereby we should without doubt obtain interesting and instructive results. This I had an op- portunity of doing in the following year 1867; and I then examined, as minutely and consci- enciously as possible with the instruments at my disposal, the structure of this little and fragile animal, which I also found peculiar inthe highest degree, and different from all that I had previously known. My Father was also greatly surprised on learning the result of my examination, and looking over the numerous drawings which I had made from the living ani- mal, It was clear enough that we had before us not only an entirely new genus and family, hut even the type for a still higher division; and we found no small difficulty in referring it to any known animal type. But as it appeared most nearly related to the Polyzoa, my Father classed it with these, and noted it in his catalogue of deep-sea animals, compiled in 1868, under the denomination of ,Halilophus mirabilis“ (the generic name taken from a certain 1 to resemblance of the tentacular arms to the so-called Lophophore of the freshwater Polyzoa). The next year appeared Allman’s treatise on Rhabdopleura, a new form of Polyzoa from deep sea dredging in Shetland“?; and my Father, as well as myself, at once recognised in the species therein described and delineated, Rh. Normanni, a form closely agreeing with the Halilophus mirabilis, but which evidently, from the form and attachment of the Polyzoarium, must belong to a different species from ours. Allman’s communications concerning the organisation of the animal shew indeed, as will appear from the sequel, many essential differences from what I have had occasion to observe in our northern form; so that if these communications were in reality correct, there could scarcely be any doubt that both forms were also generically distinct. But the-fact is that Allman has only had the opportunity of examining specimens preserved in spirit; and both my Father and myself know from experience how extremely difficult it is to obtain results with specimens in this state, and what imperfect and false notions may thus be formed of the animal’s real structure. Taking this into consideration we may really be astonished that Allman has been able to see so much as he actually has seen, and that he has not misunderstood the animal’s organisation in a greater degree than appears from his description and delineations. Allman has indeed seen in the Rhabdopleura avery aberrant form of Polyzoa, but is far from having apprehended that the form is ab- normal in so high a degree as it is proved to be, according to investigations which I have executed with the utmost care and minuteness. With respect to the method of examination, there is little or no use in dissecting so small and fragile an object as the animal of the Rhabdopleura, even if the finest imaginable instruments are employed. It is therefore necessary to study the animal entire as it is, or at most after separating the individual animals from their cells or tubes, which, as will be seen, may be done with the greatest ease in operating on the living colony. In order to get a better and sharper view of certain parts, I have found it very useful to effect a gentle com- pression of the animal between 2 glass plates, but so that the pressure can be moderated at will, increased or diminished. To this end I cemented a thin glass plate to the upper arm of my compressorium, by which means the desired result was obtained far better than by the use of the so-called aquatic boxes“. Moreover most of the parts of the living animal may be easily examined without pressure, and without even taking the animal out of its cell. A colony, or part of one, can be placed under the microscope, and the most important parts will plainly be seen through the transparent walls of the cells, even if the animal has not stretched itself out of the aperture. Besides the outer chitine-like tube with its off-shoots or cells (Polyzoarium) there may be distinguished in the animal under consideration the following principal parts. 1. the Po- lypide itself, which again shews 3 principal parts a) the body; b) the tentacular arms and c) the bueal shield; 2. the contractile cord; and 3 the arial cord. We shall treat each of these parts separately. * Quarterly Journal of microscopical science. Vol. IX. 1869. p. 57—63. pl. 8. The Polyzoarimn. The Polyzoarium (ccencecium) in the Rhabdopleura mirabilis (see fig. 1. 2. & 3.) has the form of a thin, elastic flexible, chitine-like, transparent. most frequently quite colorless cylindrical hollow tube, consisting of a stem which creeps along the bottom of the sea, now and then attached to other bodies, irregularly winding, and only seldom, here aud there, forked. which at short intervals sends up perpendicular, free, undivided, more or less winding branches or continuations, of the same form calibre and nature as the stem, and all terminating with a circular aperture. A difference between the stem and the branches, strikes the eye imme- diately: the stem is always more or less thickly covered with extraneous particles (sand, mud, fragments of shells, Rhizopod-shells &c.) while the branches are always, with exception of the very lowest piece, quite free from such particles, and consequently quite transparent, appearing in their whole extent very distinctly and ornamentally ringed. The rings, which are only exterior, form close, equidistant, sharp, circular transverse folds, strongly prominent over the surface of the tube, causing the edges everywhere to appear crenulated (see fig. 3). If one can sepa- rate from the stem the very closely adhering extraneous particles, (which is connected with no small difficulty) it will be seen (fig. 9) that this outer formation of folds is also continued on the stem itself, althongh far less sharply marked and also more irregular: the transverse folds being often divided fork-wise, or in other words, not forming completely separate rings. It will also be remarked (fig. 10) that the branches or free tubes are not at all sharply dis- tinguished from the stem, but that their interior cavity is prolonged immediately into, or continuously with, the cavity of the stem. This latter, the interior walls of which, like those of the tubes, are quite smooth, is divided at certain intervals, by tolerably thick transverse lamelle, or septa, into several successive cylindrical chambers, which do not communicate with each other, but each one of which is continued immediately in one of the perpendicular tubes proceeding upwards from the stem. Through the whole of the creeping stem, exten- ding along through all its chambers, runs a thin cylindrical chitinous cord (the axial cord) very remarkable from its dark nearly black color, of which more hereafter. This cord is never continued up through the free tubes, but may now & then, rarely, divide itself fork-wise, namely when the creeping stem divides itself in this manner. Eyery one of the perpendicular branches or tubes contains an animal, which is connected by a long cylindrical fleshy cord (the contractile cord) near the bottom of the corresponding chamber in the stem, with the axial cord, which thus unites all the individuals of the colony with each other. " The creeping stem in the Rh. mirabilis may indeed attain a very considerable length; but it is very difficult to get the whole separated from the substances which adhere to it. One can usually therefore only get up small pieces of the colony, and seldom more connected portions. The largest connected piece of stem (fig. 1) which I succeeded in getting loose from its attachment, was abont 40 millimetres long, and was at irregular distances - times bifur- i cated; another piece was of about the same length, but only 3 times divided. These bran- ches, which proceed from the stem at a more or less acute angle, are also creeping and irregularly bent, and, like the main stem, produce cells, the number of which in all on these pieces of stem amounts to about 60. The stem is thus only seldom branched, and usually runs to great length without producing any branch. The cells or tubes, which proceed from the stem by lateral budding, are of very dif- ferent length, while their thickness is everywhere, and in all, about the same. The largest are 6—7 millimetres long and 1/,—1/, mill. thick. They are, as stated, erect, yet seldom, or never perfectly straight, but always more or less bent in some part, or in the whole of their length: sometimes like anS, sometimes in several bends or turns like a drawn out screw, but most frequently irregularly bent, in rare instances so strongly curved that the curve is nearly circular. From the above description it will be seen that the Polyzoarium in the Rhabdopleura mirabilis is decidedly different from that of the Shetland Rh. Normanni. Firstly, the cree- ping stem of the latter, of which one surface everywhere adheres to old shells or other solid substances, is much more strongly branched (,,subalternately*) and, like the cells, quite naked, without trace of attached extraneous particles. Then the cells themselves are not, as in our species, free in their whole length, but at the base for some distance, like the stem itself, fixed and creeping, for which reason also the free perpendicularly rising ringed part of the same is much shorter than in the Rh. mirabilis. Finally there appears some difference be- tween the two species with regard to the manner of the division of the stem into chambers. The Polyzoarium in the Rhabdopleura does not coincide with any other species of Polyzoa. The cells in their tubular form resemble most those of the Cyclostomata, but are horny or chitine-like (in the Cyclostomata they are chalky) and are distinguished by their surface, covered with prominent transverse folds or rings which are also foreign to the Po- lyzoa, but are found in many Hydrozoa such as certain Tubulariade and Campanulariade. The Polypide. The individual animals or Polypides seem at first glance to resemble the ordinary Po- lyzoa (see fig. 3). The body, which is only a little over 1 millimétre long, is oblong, and appears to be occupied almost entirely by the digestive system; on closer examination, we find however (see pl. 2. fig. 15, 17, 18) that a thin glassy skin surrounds the digestive appa- ratus, which therefore is not, as in all other Polyzoa, freely suspended in the ,,Perigastric fluid“, which Jatter, as will appear in the sequel, is entirely wanting in the Rhabdopleura. In all other Polyzoa without exception there is besides the so-called Ectocyst, corresponding with the Polyzoarium, also a so-called Endocyst, which always represents a thin membrane lining the interior of the Ectocyst or cavity of the cell, and, from the aperture, recurved and attached round about to the Polypide under the base of the Lophophore. The interior cavity of the cells in the other Polyzoa is thus actually completely closed by the endocyst and the 5 body of the Polypide; and the so-called perigastric fluid therein contained, wherein, the intes- tinal canal of the animal is freely suspended, does not stand in any direct connexion with the surrounding medium. The retraction of the Polypide into the cell is effected only, by a folding (invagination) of the anterior elastic part of the endocyst, by which the so-called ten- tacular sheath is produced. The case is quite different with the Rhabdopleura. Here is no endocyst at all (unless we should consider the glassy skin which closely surrounds the diges- tive apparatus, to be an endocyst), consequently also no perigastric fluid; and further the cavity of the cells stands in direct communication with the surrounding medium, without being closed at the aperture by a skin connecting it with the animal’s body. The retraction and protrusion of the Polypide is therefore not effected as usual by in- and evagination, but in a totally different manner, of which more hereafter. Allman has indeed (1. c.) imagined that he has perceived a trace of a real endocyst of the same nature as that observed in the other Poly- zoa, but he has quite certainly deceived himself. The Polypide of the Rhabdopleura lies quite free in the cell, and is only attached to the colony by means of the contractile cord, neither by any endocyst nor special muscles, as appears clearly enough from the fact that when the contractile cord is severed, the Polypide can be taken entire and uninjured out of its tube with the greatest ease. From the anterior part of the body where the mouth is situated, yet, as will appear in the sequel, not as usual in a terminal position, but rather in a ventral situation behind the peculiar oval prominence (the bucal shield), the gullet or wsophagus, (fig. 5, 14 etc. e) rather short, but wide, and furnished with thick walls, proceeds right downward or backward to the stomach, from which it is separated by an also outwardly apparent constriction, and by a sort of internal valve (the cardiac valve). The Stomach (f.) which is simple without any armament of teeth or hard parts in its interior, and furnished with tolerably thin walls, is elongated, rounded cylindrically, slightly and somewhat irregularly curved, with ventral concavity, and in its anterior part, where it has its greatest breadth, only a little wider than the gullet and occupying about */, of the cell’s caliber (see fig. 14). In the anterior half it is of about uniform thickness, but diminishes towards the posterior end (Pylorus) very rapidly, and goes imperceptibly over, after turning a little to one side, into the intestine, suddenly curving itself wpward and forward. The Jn- testine (g) which is not by any constriction, nor yet by any interior valve (Pylorus-valve) dis- tinguished from the stomach, of which it forms the immediate continuation, is narrow, cylin- drical (its thickness scarcely 1/, of that of the stomach in the widest part) only slightly tapering towards the end (see fig. 17) and has a tolerably straight course forward, lying close, to the dorsal side of the stomach and gullet, and terminates with a circular anal aperture, situated just behind the spot from which the tentacular arms proceed. Immediately behind the anal aperture, between the terminal part of the intestine and the dorsal wall of the gullet, which here forms a little concavity, there appeared a clear cellular body (fig. 15. r) in which several evident nuclei were visible. I cannot however pronounce any decided opinion as to the signification of this object; it can scarcely be a nervous ganglion; as it does not lie in the substance of the body itself, but only in the thin external skin which encloses the body. The stomach and the intestine usually shew in the living animal a bright opaque yellowish brown color, which color seems mainly to be derived from the contents. When the stomach and intestine are more empty, they shew a far paler yellowish white color. The walls of both shew plainly a fine cellular structure. It is evident that the digestive system in the Rhabdopleura differs, in many points which have not been remarked by Allman, from the normal system of the Polyzoa. In the latter the stomach usually consists, as_is well known, of 2 distinctly separate parts, one shorter cylindrical cardiac part, and a longer and wider pyloric part, which ends in a large rounded bottle-shaped Caecum (cul de sac). Therefore the intestine usually takes its origin, in these, high up, or about on a level with the transition of the cardiac part to the pyloric part; while in the Rhabdopleura, where no such division of the stomach occurs, the intestine proceeds from the posterior end of the stomach or fundus, as the immediate continuation of the same. The Tentacular Arms. ' The tentacular Corona, or Lophophore, situated in the Rhabdopleura on the anterior end of the body, is of a totally different appearance from that of the other marine Polyzoa, while on the other hand it appears at first sight to shew an unmistakable resemblance to that of most fresh-water Polyzoa (P. hippocrepia) and is also thus represented by Allman. However when it is more closely examined, it displays many essential differences; althongh by its strongly marked bilateral symmetry, it appears to be most nearly connected with the same, in respect of the semilunar or horse-shoe form peculiar to them. As in the said fresh-water Polyzoa, the léphophore or tentacular frame does not form a circular ring, but is drawn out into 2 lobes or arms, each of which bears a double row of tentacles. These lobes or arms (fig. 3. 4. 5. &c. d.) which also here proceed from the dorsal side, are however considerably longer and narrower, or more cylindrical than in any other of the known Polyzoa; and while in those freshwater Polyzoa they only form a part of the ten- tacular corona, they represent here the whole lophophore, as it is only on these arms that the tentacles have their place. The tentacles in the Rhabdopleura do not form, as in the other Polyzoa, a continuous series, but are interrupted, as well dorsally as ventrally, by an evident interval; in other words, we have not one single tentacular crown, but 2 symmetrical tentacular arms, which take their beginning on each side of the anterior part of the body, and extend out from the same dorsally and diverging to each side. If we examine these tenta- cular arms in the living animal we find that they are also in many respects different from the lophophore of the Hippocrepia. While the latter always retain unchanged their form and somewhat inclined direction, the tentacular arms in the Rhabdopleura are in a high degree flexible and variable in their direction relatively to the body of the polypide and to each other. As long as the polypide is withdrawn into the cell, they are always (see fig. 14), — ~l extended straight forward, and nearly parallel with each other, forming, together with the tentacles attached to them, a close fascicle extending in the same line with the body. As soon as the polypide reaches the aperture of the cell, they spread out from each other; but this takes place in various manners. Sometimes they are bent with the ends only a little out from each other, while otherwise they are nearly parallel (see fig. 3.); sometimes they spread themselves out so widely on each side, that they stand almost diametrically opposite (fig. 4); sometimes they bend themselves with the ends downwards (see fig. 3); sometimes — and this is most usual, and always occurs when the animal is taken out of its tube (fig. 5), they are bent upwards and backwards, and that often so strongly that they describe a nearly semicircular curve, so that the extremities even touch the dorsal side of the polypide’s body (fig. 5 & 15). This great mobility of the tentacular arms or lophophore (so different from what is observed in the other Polyzoa) which appears to be produced at will by the animal, sometimes in one manner and sometimes in another, must certainly, although it always takes place very slowly and with little energy, be brought about by means of auxiliary muscles or muscular tissue. I have however only succeeded in observing very faint traces of anything of the kind: When the animal is gently compressed between 2 glass plates one may observe on each side some very fine fibres (Fig. 15, 18, p) passing obliquely over the gullet, proceeding from the ventral side, where the body of the polypide forms on each side a small conical prominence (ibid. 0.0.) which may perhaps be considered as the ventral corners of the lophophore, and losing themselves at the root of the tentacular arms. They appear to represent the retractile muscles of the tentacular arms, which produce their. flexion upwards and backwards. It has not been possible for me to discover any distinct trace of any such thin membrane connecting the basis of the tentacles (the so-called calyx) as is found in the fresh-water Polyzoa. As regards the ¢entacles themselves, they are indeed (fig. 8) of the usual cylindrical form for Po- lyzoa, and are as usual furnished with cilia; but in the living animal they have a very different appearance from that of the tentacles in the ordinary Polyzoa. While in the latter they are always in the greater part of their length extended straight, forming a regular corona (see tab. 2. fig. 28. & 30. d.) which only slightly changes its form, the end of some one or other of the tentacles being only sometimes bent a little in one direction or another, the tentacles in the Rhabdopleura are always bent and curved in the most irregular manner in all directions (fig. 4. 5. 15. 18) so that there can be no question of any regular tentacular corona. The number of these tentacles, which as above mentioned, are attached in a double row along the anterior side of the tentacular arms, is somewhat various (about 40 on each arm); they are longest about in the middle, and are in this part about 1/, of the length of the arm, and di- minish somewhat towards the base, but more towards the extremity, where they are often quite rudimentary. The tentacular arms themselves, each of which at the base on the dorsal side, is furnished with a little fascicle of unusually long cilia attached to a small tubercular prominence (fig. 15. 17. n) are of very considerable length, quite as long as the whole of the rest of the body; of narrow cylindrical form, thickest at the base and tapering regularly to 8 the end, which is obtusely pointed. Anteriorly they are separated (see fig. 16) by a naked, somewhat concave part, (extending a little downwards) here contiguous to the basis of the remarkable oval shield (c) which, both by its enormous development, and peculiar function, below described, forms one of the most peculiar features of the Rhabdopleura. The Bueal Shield. Between the bases of the tentacular arms, and from a somewhat ventral point, pro- ceeds in an anterior direction, a large and very remarkable prominence (fig. 4. 5. &e. ¢) situ- ated longitudinally, which has the form of an oblong thick disk or shield, one surface of which (the dorsal surface) is in the middle grown together with the anterior end of the body, while the ventral surface is free and bordered by a rather thicker raised ridge, distinct from the adjacent parts. The form of this disk is, as above mentioned oval, or rather rounded pen- tagonal (see fig. 18. c) nearly half as long again as wide; the width about equal to that of the body at the beginning of the stomach. Its posterior border, which at once shews itself (see fig. 5) separated by a deep constriction from the part of the body lying behind it, is in the middle slightly incurved (fig. 18). The side borders are, a little in front of the middle, strongly, almost angularly bent, and then converge strongly. towards the anterior freely projec- ting extremity, which is narrowed obtusely. The whole disk is everywhere, and especially distinctly on the edges, thickly covered with small vibratory cilia. Allmann, who also mentions this prominence, but without having gained a correct notion of its form and connexion with the other parts, says of it that one might take it for a large and peculiarly developed Epi- stome, if its position on the ventral side of the mouth, and not, as in the fresh-water Polyzoa, between the mouth and the anus, did not oppose such a supposition. Allman supposes thus that the mouth in the Rhabdopleura, in analogy with the other Polyzoa, is terminal, and situ- ated above, or on the dorsal side of this promimence, between it and the anus. Such is how- ever not the case. The anterior extremity of the body above the prominence described is completely closed without any trace of aperture (see fig. 16). On the other hand I have by gently compressing the animal, been able distinctly to see (see fig. 15) that the bucal aper- ture (q) is situated just on the ventral or hemal side behind that prominence, and seems to have the form of a cross slit, which is bordered behind by an oval lobe (m.) furnished with vibratory cilia like a sort of underlip. By increased pressure the bucal shield could be moved more out from the base of the tentacular arms; and it appeared then everywhere very dis- tinctly constricted from the rest of the body, and in the middle of the dorsal surface, fixed to the body by a sort of short stalk, while the upper and the lower part were free. Further it was observed that-on each side of the bucal shield there extended, from the base of the tentacular arms downwards, a strongly projecting nearly semilunar border of thin skin (I) ciliated on its edges, so that between this and the bucal shield there is formed, on each side, a narrow half-tube or channel leading to the bucal aperture, and through which the nourish- ment is probably conveyed to the mouth by the abundantly ciliated tentacles. Since, as above g stated, the said bucal shield is really situated between the mouth and the anus, I think we may consider it as morphologically answering to the so-called Epistome im the fresh-water Polyzoa. Its enormous development in the present instance seems however to indicate that it must have a very peculiar and important function in the economy of this animal. My ob- servations on the living animal have also guided me to a decided opinion, to which, however strange it may appear, I have been forced again and again to return, and which I therefore must retain: namely that the animal uses this bucal shield (according to my observations), as a sort of ereeping-organ, by means of which it can draw itself up to the aperture of its tube. Since, as above stated, both Endocyst and all muscles of protrusion are wanting, it is in rea- lity quite inexplicable how the Polypide, which is often found drawn back, not only to the bottom of the free cell, but even partially into the corresponding chamber of the creeping stem, (see fig. 10) should be able in any other manner to get forward again so far as to the aperture of the cell. It might perhaps be supposed that this could be effected by means of the elasticity of the contractile cord; but I have convinced myself that such is not the case, by cutting through the contractile cord at its base; the Polypide has continued undisturbed its slow protrusion, and has also at length really reached the opening of the cell without any remarkable change.. The direct observations made on the uninjured animal have also con- firmed me in the view expressed above. It will be seen (see fig. 14) that during the slow protrusion of the Polypide (which often lasts for hours) the bucal shield is always in imme- diate contaet with the wall of the tube, the whole of its ventral side being closely pressed up against the same; it retains this position unchanged as long as the protrusion lasts; and the protrusion does not stop until the whole length of the bucal shield is extended out- side of the aperture of the cell; then the Polypide is completely expanded. On examining more closely this bucal shield (see fig. 4) we observe in the middle of it an opaque part which seems to contain an interior glandular organ. Continuing the investigation, and slightly pressing the animal, we notice however (fig. 18) that this opaque appearance is not produced by any such internal organ, but by a peculiar and seemingly muscular structure of the sub- stance of the shield itself. It exhibits, seen from below, in the middle numerous small bub- bles situated rather far from each other, or somewhat irregularly formed small cells, which however when more closely examined (and this is particularly evident in those which lie nearer to the periphery of the disc) shew themselves to be the external rounded extremities of small inwardly prolonged cylinders, which together appear to form a thick fascicle of incompletely differenced muscular fibres penetrating into the stalk of the bucal shield. The animal is, with the aforesaid exception of the stomach and the intestine, which are opaque yellow, colorless and transparent. The tentacular arms, and the tentacles, as also the anterior part of the body before the stomach, are covered with numerous very small irre- gularly shaped intensely dark violet spots of coloring matter which also occur on the bucal shield, and expecially on its anterior freely projecting extremity, where they are very close together, forming a large roundish dark spet. In specimens in spirits all these parts are 9 10 dark reddish brown, which probably arises from the diffusion of the dark coloring matter produced by the spirit. The Contractile Cord. As above stated, the Polypide is without any sort of attachment to the cell, in which it lies quite free. But it is attached by means of a long and thin fleshy cord to the axial cord which runs through the creeping part of the Polyzoarium or stem. The attachment does not take place immediately at the bottom of the free cell, but at the bottom of the corre- sponding chamber of the creeping stem, close to the transversal septum which divides the chamber from the next preceding (fig. 10 & 11). This cord, issuing from the body of the Polypide (tig. 3. 5. 10 &e. h) is of very considerable length; as, when the Polypide is expan- ded, it extends not only through the whole length of the cell, but also through the corre- sponding chamber of the stem. The cord is however very thin, filiform, when fully extended 5 or 6 times less than the caliber of the cell, and 4 times thinner than the stomach. It is of cylindrical form, and lies quite free without being attached at any point to the wall of the cell; but it is nearer to the one side (the ventral) than to the other. Along all one (the dorsal) side it is covered with the same sort of small dark violet spots of coloring matter as the anterior part of the body, the tentacular arms &c., but is otherwise quite colorless and transparent, and is of a soft fleshy consistency. It shews on closer inspection, (see fig. 7) in a part of its substance, an extremely fine fibrous structure of fine parallel longitudinal lines and less sharply marked transverse lines; but in the dorsal part these fibres are entirely wanting; and the structure of this part seems to be cellular, and its edge appears somewhat irregularly wavy. With regard to its attachment to the Polypide, this does not take place at the bottom of the stomach, but rather high up on the ventral side where it ‘ seems to go over into the thin skin which encloses the digestive apparatus.. Its ventral fibrous part may still be traced (see fig. 15) to a considerable distance forward, in the form of a rather wide clear skin-border which gradually disappears in front of the Cardia. In this skin-border, the fine longitudinal fibres may still be distinctly observed diverging like radii; but I was not able to trace their course further. The posterior end, which as beforesaid is attached to the Axial cord at the bottom of the chamber in the stem which corresponds to the cell, is (fig. 6) somwhat enlarged; and all through of a very distinctly marked cellular structure, without any evident fibre. In spirit specimens, the contractile cord: shews itself often irregularly thickened in particular places, and is also thus represented in Allman’s figures; but this appears to be only a result of the action of the spirit. .In living exemplars I have always found it, whether fully extended or contracted, of a cylindrical form. When the Po- lypide, as is frequently the case, is very strongly retracted, not only to the bottom of the free cell, but also partly in the corresponding chamber of the stem, the contractile cord is always spirally convolved, so that the coils are closer or looser, accordingly as the retrac- tion is stronger or weaker (see fig. 10). Also when, after severing the contractile cord 11 at its base, we take the animal out of its cell (fig. 5), the cord always convolves itself in spiral coils. Allman has considered this contractile cord as corresponding with the socalled funi- culus in the ordinary Polyzoa; although it is not as in these, attached to the end of the stomach (the terminal cecum), but on the ventral side of the Polypide’s body (Allman has represented it erroneously as attached near the end, on the dorsal side). Moreover Allman indicates that this funiculus is accompanied by a long fascicle of muscular fibres attached to the chitinous cord (axial cord) at the point where the funiculus is joined to the same; and that at the point where the funiculus is joined to the animal’s body, this muscular fascicle divides itself in 2 bands, of which one goes along the right side, and the other along the left side of the body, finally attaching themselves, each on its own side, to the Pharynx below the Lopho- phorus. These fibres form, according to Allman, the great retractor muscles of the Polypide. This representation, which in fact only depends on spirit specimens, does not, as may be seen, agree with what I have had occasion to observe in our northern species, in which the fascicle of muscles (if one really may venture to use this appellation here) is everywhere, as an integral part, intimately connected with the contractile cord, and is produced only by a peculiar modification of its tissue on .the ventral side. Special retractor muscles cannot there- fore, any more than other muscles, be said to be distinguished in the Rhabdopleura. The Axial Cord (,,chitinous rod‘ Allman). Through all the creeping stem there extends, as already mentioned, a filiform cord very remarkable by its dark, nearly black color, and, unlike the contractile cord, to which it is about equal in thickness, only slightly flexible, and of a very hard chitine-like consis- tency. This cord (fig. 3. 9. 10. 11 &e. i) which we will call the axial cord, is freely extended in the hollow of the individual chambers into which the stem is divided, and only attached to the septa, which it perforates enlarging itself a little (fig. 11). In conformity with the rarely branched form of the stem, it is only now and then forked; and when this takes place, - it is always at one of the septa. Otherwise it forms everywhere a cylindrical tube with very strong, almost horny walls, but always enclosing in its interior (see fig. 12) a soft cellular cord (s) of similar appearance to the contractile cord, and’ like it colorless and transparent with small dark violet spots of coloring matter, but scarcely half so thick. This fine cellular marrow which extends through the whole length of the axial cord, seems entitled to be con- sidered as a sort of incompletely defined nervous trunk connecting all the individuals of the colony; as at each partition in the stem, it sends forth a branch which enters into the con- tractile cord of each respective individual animal; and the latter cord does also probably contain in its dorsal part the imperfectly developed elements of nerves. We may therefore herein observe the analogon of the so-called Colonial Nervous system (so strongly developed in the other marine Polyzoa) and specially in the marrow of the axial cord, the common main trunk of the whole colony. O* Allman, who has drawn special attention to this peculiar chitinous axial cord, (which does not exist in any of the known Polyzoa), and has precisely derived from it his generic appellation, calls it a ,,Blastophore* being of opinion that it is destined to bear the so-called Statoblasts, which he represents as projecting from the posterior part of the contractile cord. I regret that I cannot, from my own experience, give any decided opinion as to the axial cord having likewise this destination, because I have not been able to observe the formation of these so-called Statoblasts. Vital Phenomena. The animal, unlike the other Polyzoa, is very slightly sensitive, and is not much af- fected by having its tentacles or body touched. If the irritation is strong, it draws itself, but only very slowly, and usually only a little way, back into its tube. This very slow and slug- eish retraction, which may last a very long time before it ceases, contrasts strongly with the extraordinary, almost lightning-like, rapidity with which the retraction takes place in the other Polyzoa, and is evidently accounted for by the want of special retractor-muscles, and by the slightly developed contractile elements, not distinguishable as evident muscular fibres, in the contractile cord, the only instrument by which the retraction of the animal in the Rhabdo- pleura is effected. The extension (protrusion) of the animal is yet far more tardy than the retraction ; the process is extremely slow and almost imperceptible; several hours may often elapse be- fore the animal progresses from the stem or bottom of the cell to the aperture of the latter. Neither do we, as before remarked, find in the animal under consideration the slightest trace of any special muscles for such progression; since the Endocyst, and also the parietal and parieto-vaginal muscles connected with it are entirely wanting. The protrusion seems on the other hand, as already mentioned, to take place in a very peculiar, and in the highest degree remarkable manner, that is, solely by means of the enormously developed Epistome (Bucal shield) which the animal uses — strange at this may sound, — as a sort of creeping organ, like the foot, or creeping disc of the Gasteropods, to draw itself upwards little by little along the wall of the cell to the aperture. Occurrence. The Rhabdopleura mirabilis seems to be a genuine deep-sea product, which I have never found at a less depth than 100 fathoms; but it is probably to be found extensively at greater depths, where it appears to be more and more plentiful. I have hitherto only found it in Lofoten, where it is not uncommon, in soft clay bottom, at depths of 100 to 300 fathoms. As the Polyzoarium is both very small and entirely colorless, it is rather difficult to discover. Its presence is however easily detected by stirring the washed mud in a fine sieve with a feather or another instrument, when irregular fibres will be noticed therein. These fibres, covered with particles of mud, Rhizopod-shells and fragments of mussel-shells, will prove to be the creeping stem, whereon by closer investigation there will be discovered the small transparent perpendicularly projecting cells. One seldom, however, succeeds in raising these colonies entire; they are most frequently broken into several pieces by the dredging operation itself, or in washing out the mud. Characteristics of Genus and Species. We may, according to the preceding description, characterise the Genus Rhabdopleura in the following manner. Gen. Rhabdopleura. Allman. Polyzoarium tubum formans tenuem, flexibilem, cylindricum, chitinosum hyalinum ex stirpe compositum repente intus septis transversis in cameras plures discretas divisa quarum utraque in cellulam cylindricam plus minusve liberam et erectam stirpe vix angustiorem sub- tiliter annulatam vel plicis acutis circularibus dense ornatam, oriticio simplice circulari termi- natam exit. Stirps in tota longitudine chorda chitinosa, obscura, tenui, cylindrica, rigida, pulpa vero molli cellulosa impleta trajecta. Polypides nullo endocysto vel pallio parietibus cellularum connexi, sed modo funiculo contractili tenui et carnoso chorde stirpis chitinose affixi, corpore forma elongato-ovata, ex- tremitate anteriore paulo dilatata et in ramos divisa duos cylindricos et attenuatos supra vergentes et a se divergentes, quibus series duplex tentaculorum flexuosorum affixa est. Se- ries tentaculorum minime continua sed et supra et infra intervallo distincto interrupta, quare nulla adest corona tentacworum vel lophophorus proprie dictu sed modo duo rami tentaculiferi valde flexibiles. Inter bases horum ramorum inferne adest prominentia magna carnosa scuti- formis ovalis vel subpentagonalis pedicello brevi et crasso affixa facie inferiore subplana ex- tremitate antica libere prominente attenuato-truncata, inferiore corpori incumbente medio leviter emarginato superficie ubique dense ciliata. Orificium oris subventrale, transversum pone prominentiam scutiformem situm, postice lobo rotundato ciliato limitatum. Qsophagus brevis et spatiosus constrictione distincta a ventriculo sejunctus; ventriculus simplex subteres, postice attenuatus et sine fine, ansam sub- itam formans in intestinum transiens; infestinum antice porrectum tenue cylindricum lateri dorsali ventriculi et cesophagi incumbens, orficio anali circulari ad basin ramorum tentaculi-! ferorum supine sito. Tractus intestinalis, vel corpus proprium polypidis, minime nudus, sed cuticula distincta, tenui, hyalina circumcirea arcte circumdatus. Musculi adsunt null distincti, neque retractores, neque protractores. Retractio Poly- pidis solummodo funiculo contractili effecta; profrusio singulari modo prominentia effici videtur scutiformi preorali, at modum sole gasteropodum. Et retractio et protrusio polypidis seg- nissima. Spec. Rhabdopleura mirabilis. (M. Sars). Polyzoarium irregulariter flexuosum sed raro modo et parce ramosum, stirpe corporibus - 14 alienis modo ex parte adherente ubique particulis alienis vel quisquiliis dense obducta, cel- lulis vero nudis in tota longitudine liberis perpendiculariter ascendentibus, vario modo flexu- osis, valde elongatis (15ies—16ies circiter longioribus quam latioribus) stirpe vix angustioribus. Habitat ad insulas Lofotenses in profunditate 100—800 orgyarum fundo limoso, non infrequens. Development. I have unfortunately not been able to make any observations on the development of the living animal, in which I have also in vain sought for the organs of generation. It was only by critically passing in review the specimens which I had brought home one by one, that my Father at last succeeded in discovering in the creeping stem a couple of polypides in course of formation. Allman has however been more successful, and has even found in the specimen of the Rh. normanni examined by him, a whole series of developments, which is of great interest. I can therefore only add very little to Allman’s communications on this subject. Both of the buds observed by me (fig. 20 x.y.) had their place in separate, every- where closed chambers of the creeping stem, without these chambers having as yet prolonged themselves into any cell, and like the developod polypides, appeared here attached to the axial cord near the bottom of the chambers at a short distance from the transversal septum. The youngest of the buds (fig. 20 x. fig. 21) corresponds approximately with the’ youngest stadium observed by Allman; as only 2 parts were to be distinguished, a short stalk and an enlarged terminal part, which had not however the form indicated by Allman of 2 compressed yalyules, but of a wide scutiform slightly curved plate (see fig. 21). The stalk (h) which is strongly, almost globularly enlarged, is continued for some distance along the concave side of the scutiform plate mentioned; but this continuation, which is not visible from one (the ventral) side, is by an evident instriction separated from the proper stalk, andrepresents the groundwork of the Polypide’s real body, whence as well the tentacular arms as the digestive system are afterwards developed. The other bud (fig. 20 y. fig. 22, 23 & 24) will about an- swer to the stadium delineated by Allman 1. ¢. fig. 6. The peculiar scutiform part (c) has also here the form of a wide evenly curved plate, which already has assumed a somewhat pentagonal form, and completely covers on one side the still only slightly developed real body, from which however there project in front 2 tentacular processes (d. d.) extending beyond the border of the shield, and slightly crenulated at the edges, representing the tentacular arms; the stalk (h), which represents the contractile cord, has lengthened itself considerably (see fig. 23.), and its anterior part (fig. 24. h) forms a strong enlargement, marked with evi- dent traces of the spots of dark violet coloring-matter peculiar to the adult animal. The real body was, as stated, still very slightly developed, and appeared only as a small rounded part projecting dorsally between that enlarged part of the stalk and the basis ‘of the tenta- cular arms; on the ventral side, or that which turned towards the concave surface of the scutiform plate, it was in the middle, and to a small extent, united to the same by growth; 15 and behind this union there appeared already an evident incurvation or incision in the body of the Polypide as the first indication of the bucal orifice. That the large scutiform plate is the homologon of the bucal shield in the fully developed Polypide is sufficiently evident, both from its position relatively to the animal’s body and from its shape. Allman has also recog- nised this; however when he assimilates this plate in the Rhabdopleura-buds with the mantle lobes of the Lamellibranchiata, the notion seems to me very hazardous and difficult to esta- blish. In any case, the early appearance and enormous development of this part in the buds of the Rhabdopleura, are extremely remarkable. Allman has — guided especially by the mode of development in the Rhabdopleura — come to the conclusion that the Polyzoa are not, as was formerly imagined, most nearly related to the Brachiopods, but to the Lamellibranchiata, and gives 1. c. some schematic figures, in order to represent more evidently the agreement of the Rhabdopleura-buds with a Lamellibranch. Allman however présupposes, as taken for granted, that the Rhabdopleura is furnished with an endocyst of the same nature as the other Polyzoa, which, as above stated, is not the case; as also his conception of the bucal shield seems to be inaccurate. As will be seen in the sequel, my Father has acquired a very different notion with regard to the relationship of the Polyzoa; for — guided by the organisation of their lowest represen- tative, the Rhabdopleura, —he has arrived at the surprising conclusion that the Polyzoa in all probability have taken their origin from the Coelenterates, namely the Hydrozoa. Like Allman, I sometimes found in the middle of the stem of the polyzoarium indi- vidual chambers which, without containing any bud in process of formation, were quite closed and not continued into any cell (see fig. 13). The interior wall of these chambers was always of very, dark horn-brown color, and so little transparent that the axial cord, also here running in the middle, was but dimly discernible through the wall. This dark color was particularly intense at one of the ends, and appeared to proceed from the axial cord fixed in the middle of the septa, and here somewhat enlarged. Its exterior horny substance seemed to be directly continued into the adjacent chamber of the stem. Allman considers these closed chambers, wherein he has thought to perceive a stratum of large polygonal cells, — of which however I have not been able to observe the slightest trace in any that I have examined, — as Statoblasts, and thinks that they are formed by the posterior enlarged part of the contractile cord. This seems to me however to be far from probable, at least in reference to the closed chambers examined by me; for they looked far more like remains of old cells decayed, owing to the destruction of the Polypide, as is found to be the case with other Polyzoa in the oldest part of the polyzoarium. Concluding Remarks. It will be seen from the foregoing description that the Genus Rhabdopleura differs in nearly all essential points from the ordinary Polyzoa, far more than Allman seems to have conceived. If we compare what is here communicated with the chief points which have been 16 briefly enumerated by various authors, for instance Allman, Hyatt &c. others, as characteri- stics of the Polyzoa in general, and which therefore are considered as essential marks most intimately connected with the idea Polyzoa, the anomaly of this form becomes so striking, as finally even to justify a doubt as to whether it really can be referred to the class of Polyzoa. First and foremost stands the want of a so-called Endocyst or Mantle, which sharply distin- guishes this form from all other known Polyzoa, all of which possess such an appendage. This Mantle is so essential a component part of a Polyzoon that it is difficult to imagine one without it. One would rather imagine the Ectocyst wanting, as this plays a far less important part in the economy of the animal, generally remaining passive, and properly only serving as a protection for the soft animal. The Mantle is likewise a characteristic for the Tunicates and the Brachiopods, which two classes have also been united by M. Edwards with the class Polyzoa, under the common appellation of Molluscoide (Hackels Himatega or Mantle-animals). Next, and as a consequence of the absence of a real Endocyst, the retraction and protrusion of the animal in the Rhabdopleura are effected in a manner totally different from that of the genuine Polyzoa: it moves up and down in its cell without being attached to the opening, not by invagination and evagination of the anterior part of the cell, and not by several sets of special separate muscles. The following remarks on the affinity of Rhabdopleura are from my Father’s manu- script notes: .The Rhabdopleura shews in many respects an unmistakable resemblance to certain Hydrozoa. Just as in these, the individual animals are not attached to the anterior part of the cells (in the Polyzoa the anterior involved part of the Endocyst is attached all round to the basis of the tentacular corona); the cells are therefore open, filled (not with the so-called perigastric liquid, but) with the sea-water entering from without; and the aperture of the cell is of a defined and invariable shape (while the cells of the Polyzoa are always closed by the attachment of the Endocyst to the basis of the tentacular Corona, and have therefore no proper opening; for what is called aperture is nothing more than the part of the cell through which the animal passes in and out). »Moreover, the retraction of the animal, effected in the Rhabdopleura by means of the contractile cord, at the end of which the animal is suspended, coincides essentially with that of the Hydrozoa in which the part corresponding to that cord (,,the fleshy stalk or axis“, ,,the intestinal canal“ (Loven), ,thke branched or unbranched Ccenenchym, on which the individual — animals are situated, and which is perforated by a canal-like continuation of the abdominal cavity of the individual animals“) is indeed usually less free (often in many places attached to the wall of the cell) and possesses a less degree of contractility than in the Rhabdopleura, but yet in some genera, f. ex. Grammaria, also nearly approaches the Rhabdopleura in these respects. On the contrary, the Protrusion in the Rhabdopleura is effected in a peculiar man- ner, and different from that of either Polyzoa or Hydrozoa, namely by a sort of creeping, executed by the preoral prominence (bucal shield) which appears to answer to the Epistome in the other Polyzoa, although in these it must have an entirely different function.“ On the other hand, the highly developed digestive system, the presence of an anus, the juataposition of the mouth and anus, and finally the bilateral Lophophore, are all characters pe- culiar to the Polyzoa, and entirely foreign to the Hydrozoa. »It is clear that we have under observation in the Rhabdopleura, a form of animal life which stands as it were in the middle between the Hydrozoa and Polyzoa, or forms a tran- sition from one to the other; one of those ,,perplexing forms“ which will not fit rightly any- where in the systems of zoologists. »When finally, and as the object of the whole investigation, we will give account of our conception of the Rhabdopleura, and decide on the class to which we will refer it, our opinion is that these questions, like so many others, can only be properly answered through the medium of the Darwinian theory. »The Rhabdopleura is undoubtedly, like many other animals which at present inhabit the greater depths of the sea, and with some of which we have in the latter times become acquainted, a very old form, which in its organisation has still retained several features from the time when the animal type that we call Polyzoa first developed itself from a lower type. »lhe Polyzoa, which most authors agree in referring to the main type or trunk (phylon) of the Molluscs are usually supposed, among the other animal types, to shew the greatest affinity with the Vermes; and they are even considered by many zoologists as not being mol- luscs at all, but as genuine worms. Their affinity to worms has however not been demon- strated by any evidence, and distinct transition-forms between the two are not known. The Rhabdopleura shews now evidently that the Polyzoa are not most closely related to the worm- type, but to the type of the calenterates, and especially to the class of Hydrozoa. The Po- lyzoa have already in the earliest primordial times (for fossil remains of them are found in the lowest silurian formations) developed themselves from the Hydrozoa by transmutation. We have in the Rhabdopleura manifestly such a form of Polyzoa in course of development out of a form of Hydrozoa. The changes which must take place in order that a Hydrozoon can be transmuted into a Polyzoon consist in the following points. In stead of the simple abdo- minal cavity of the Hydrozoa, with a single aperture which functions as both mouth and anus, there is formed an intestinal canal with special walls, dividing itself into 3 sections: gullet, stomach and intestine, which last ascends alongside of the stomach and gullet, terminating with an exterior aperture or anus in the vicinity of the mouth. This formation is completed in the Rhabdopleura, but no more. The following phases of this development which consist in the formation of a wide sack-like contractile Endocyst or mantle, which in its anterior part is detached from the Ectocyst or cell, involved in itself (invagination) and attached round about the basis of the tentacular Corona, (formation of the tentacular sheath, vagina) whereby the animal that formerly was free in its cell now becomes attached to the anterior part of the cell, and the complicated system of special retractor and protractor muscles, all these muta- tions have not yet taken place in the Rhabdopleura. This animal has thus remained statio- nary in the first stage of development from a Hydrozoon to a Polyzoon, but must nevertheless 3 18 be considered as belonging to the type (trunk) of the Polyzoa, since the accomplished de- velopment of its completely organised digestive system, which is so entirely foreign to the Hydrozoa, sufficiently stamps it as a Polyzoon. »Finally we remark that it may appear. strange that the Rhabdopleura, which in all probability is of so ancient origin, should possess a similar, although modified, form of ten- tacular Corona (bilateral) to that which belongs to most fresh water Polyzoa (P. hippocrepia, Gervais, Phylactolemata Allman) and which is usually considered as a more perfect formation than the circular (in P. infundibulata G). It is however possible, that the first is properly the original form, from which the latter has subsequently arisen. The fresh waters appear, as Heckel lately has remarked, to contain the direct descendents of some of the eldest animal forms which, by reason of the less complicated accidents of the fresh waters, have often in the ,struggle for life“, only slightly altered their original more simple structure; as for instance: among the celenterates, the Hydra; among the Rhizopods, the