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ESS Fy St ¥ ig re l ' } ‘ ‘ oy a 7 a a ‘a u r 1 Py » + ‘ i ‘ 1 Co ’ i - 1 P > ' ’ “ay i ' ab : - b a; ' i ’ rT 1 ie ‘ f | = j ye i a ‘ - t hy le 7 (aK rt Ji sition oF Mota Section) Library Be AviT vag : a i ;° a ; f on at Peat ‘ i he ‘a py ual if se J GRIFF Division of Mollusks Sectional Library = i ( ( % ) Wy | rh eT | i Ly} t i 4 + : 1, iy i} t aly sh i Be kid [ x pa i q il i i I i . % Y ' i gua aS Hy rh oe sey \* by “~ t Ph oy h tf He ‘ ‘ is | ‘ .) : ~ sl aAay . Wa Sy ee aN hee UR eS my : A 4uthn OVATE WIE Paes tye ene v * A ney t ' hi Li Phe Fi \ . : ee ee ; te) mR Oe eee Neue ba : te és gy r | ES Re we \Mic. a “ : wn 7 ay ee! bay ama saat v } han Si, ’ * “s x t ul : is iy y nye i \ ‘ae ae f ig tA r y ‘ eas: “ t Re i |, i watt 3 1 vy ie A, y ie ; uf ; ‘ ~ \ } if : ig 3 x : Fat ¥ & Xr WASHINGTON: Wit ss ANN abe Pact tg: ay f+ ag A PAM 4 x fl Sa a ‘ ; i ; Wega 1) GOVERNMENT PRINTING OFFICE = RAT REARS PMU ee Sin NEO 8 Sy IS ARP Na hcg 4 z eka Piston STN ee LU iS aS BAGO Rayan a oF ny ee u , ‘ : RY) Vv ; °: " 4 San sh u si ¢ 5 + Ds, apy , : . si Eee VME MOL RS OF THE NATIONAL ACADEMY OF SCIENCES. N\A olume. NL TL. 1942294 NOEMIP sk MUS IMOuO Rt WANS ELT NIG ON: GOVERNMENT PRINTING OFFICE. 1900. ny. VS . NATIONAL ACADEMY OF SCIENCES. Volume VIII. Diviion of Moflus : FIFTH MEMOIR. a ANATOMY OF NAUTILUS POMPILIUS. THE ANATOMY OF NAUTILUS POMPILIUS BY LAWRENCE EDMONDS GRIFFIN, Bruce Fellow of Johns Hopkins University. [Communicated by Prof. WiLLIAM Kerra Brooks.] INTRODUCTION. In the year 1890 Mr. Louts F. Menace, of Minneapolis, Minnesota, generously enabled the Minnesota Academy of Sciences, of the same city, to make scientific collections in the Philippine Islands. Prof. Dean C. Worcester and Dr. Frank S. Bournes made the expedition to the islands for the Academy, gathering in the course of their three years stay a large collection of scientific material. Certain anatomical material was comprised in the collection. This the Academy placed at the disposal of the Department of Animal Biology of the University of Minnesota. In the collection of anatomical material were sixty-six specimens of Vautilus pompilius. It is these specimens which Professor NacuTries allowed me the privilege of studying after I came to him as a student of zoology, and upon which the following paper is based. While the specimens were not sufficiently well preserved to allow of histological study throughout, they were, for the most part, excellently preserved for anatomical study, Professor Worcester haying taken care that they should not be contracted, and that they should be as well preserved as the circumstances permitted. Some of the external parts, however, were found to be in good order for the study of their microscopical anatomy, if not for cytological study. My studies upon the Pearly Nautilus were commenced at the University of Minnesota, under the guidance of Professor Nacurries. I wish to express my indebtedness to him for the rare privilege of studying this material, in which I have found great pleasure as well as profit, and to thank him for much kindness and many helps in the course of my work. The work has been completed since I came to Johns Hopkins University, and I wish to express my gratitude to Professor Brooks for his interest in my work and for advice and assistance which have enabled rhe, I hope, to correct or to avoid some of the faults to which my inexperience lays me liable. Professor WorcEsTER has also been very kind to me in furnishing me with what information he possessed in regard to the occurrence, habits, and mode of capture of the Nautilus. The soft parts of the Nautilus remained unknown until the year 1852. It is true that long before this Rumen had published a figure of the animal, accompanied by a description of its habits and portions of its anatomy, but the figure is not remarkable for its clearness, and the description was unintelligible until elucidated by the figures and accounts of later observers. At a later date than Rumen, Quoy and Garmarp published a notice regarding what they supposed to be a portion of the body of a Nautilus. In the year mentioned Owen published his famous Memoir on the Pearly Nautilus. This still remains the best work which we have upon the anatomy of Nautilus. When we consider 103 104 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. that Owrn had but a single specimen for dissection and no guides in his work, we can not but recognize the patient genius which enabled him to produce so complete, clear, accurate, and enduring a work. The work of VALENCIENNES (1841) added to our knowledge minor facts which OwENn had not described, beside correcting OWEN ina few slight errors. Both these anatomists had female specimens. VAN DER Horven (1848, 1856) was the first to dissect and describe a male Nautilus. Between then and now numerous papers have appeared treating of various points in the anatomy of Nautilus. But still its development is entirely unknown. Only recently WiiLEy has spent a considerable time in New Guinea in the endeavor to obtain its embryology. He has published a number of interesting papers upon details of its anatomy and its habits, and has succeeded in obtaining fertilized eggs, but has so far kept silence regarding their development. Such a paper as my own may seem superfluous to many in view of the numerous papers which have already been published upon the same subject. But I hope that it will have a useful place since I have endeavored to gather together the various disconnected accounts of Nautilus anatomy and, adding to them what new facts 1 have been able to discover, to publish an account of the gross anatomy of Nautilus which shall be as complete as possible. Few persons have the opportunity, and still fewer the time to examine all the various papers on this subject, so I hope that, beside adding to our knowledge of Nautilus, this paper may be found convenient by the student of comparative anatomy. Although the shell of the animal might properly be considered in an anatomical description, in this case it is so well known that another description of it by me would serve no good purpose. The Nautili of the Menage collection were captured in water of 1,800 feet depth off the south- ern coast of Negros, Philippine Islands. An extract from a letter of Professor WORCESTER to the Minnesota Academy of Natural Sciences tells of the mode of capturing the animals. ‘Their (the natives’) method is to lower a large bamboo basket, baited with meat, in six or eight hundred feet of water. This basket is made on the principle of the old-fashioned rat trap, allowing the animal to enter easily but preventing its escape. Every morning these traps are drawn up for inspection, and a single one sometimes contains four or five live Pearly Nautili; which are sold for food, bringing about 4 cents apiece.” This was written after a preliminary examination of the ground, but several months before the capture of the specimens which were sent to this country. The specimens taken by the expedition were caught in deeper water than that mentioned in the letter. The natives ordinarily set their traps for a deep-sea food fish, the capture of the Nautili being in a measure accidental, at most, incidental. Nautilus is not confined to deep water. It has generally been found there, but Wi1LEyY has also obtained it in water only 2 or 3 fathoms in depth. Nautilus is carnivorous, and apparently predatory, the crop and stomach of captured specimens being usually filled with fragments of crustacea, or the chicken, or fish, or whatever other meat is used for baiting the trap. The appearances indicate that it feeds mostly upon a species of decapod crustacea. These are devoured shell and all. The jaws appear strong enough to erush any moderately thick-shelled mollusk upon which the Nautilus might happen. Witiery (1897, 1) says: ‘One of the surest ways of obtaining Nautilus, and in fact, the method by which T have obtained most of my specimens at Lifu, is to bait the fish basket with the cooked and bruised exoskeleton of Palinurus, or an allied form. The strongly scented *potage’ so produced is then wrapped up in cocoanut fibre like a small parcel, and then placed in the fish trap overnight. There is therefore nothing to be seen, but on the other hand there is something to be smelt, and by this means I have obtained as many as ten Nautili at one time.” While this observation points to the probability of Nautilus being chiefly guided by its sense of smell in the capture of its prey, it is not by any means proof that the eyes are not also useful in this action. We would rather expect that smell would be the guiding sense from the fact that the Nautilus is usually found at great depths where darkness must prevail, and from the simple character of the eyes. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 105 GENERAL SKETCH OF ANATOMY. The Nautilus occupies a light gracefully formed shell, which is beautifully marked with alternating bands of reddish brown and white, except near the mouth, where the dark bands do not interrupt the white ground. (Fig. 11). The shell is coiled dorsally (exogastrically) so that the older parts are completely hidden by the younger. An adult shell has about two and a half whorls, As the Nautilus increases in size it grows forward in its shell, leaving an unoccupied space behind itself. At frequent intervals it forms septa which completely separate the unoccu- pied portion from the living chamber of the shell, except at the centers of the septa, where they inclose a tubular process of the body wall, which extends to the oldest chamber of the shell. (Fig. 1.) The unoccupied chambers of the shell are filled with a gas which resembles air in its composition, but haying a slightly greater proportion of nitrogen than the latter. When the Nautilus is in its natural position the involution of the shell is uppermost, while the mouth of the shell is below and turned forward. (Fig. 1.) The body is now nearly horizontal: the head, surrounded by tentacles, is anterior; the siphuncle is near the posterior end of the body; the funnel is upon the ventral side, and the depression which receives the involution of the shell marks the dorsal side of the body. (Fig. 2.) The orientation of the body and the description of the anatomy are made more difficult by the upward curve of the posterior part of the body. Thus, the siphuncle springs from the dorsal surface near the posterior end, and not from the extreme posterior end of the body. (Fig. 2.) The body of Nautilus is roughly oblong, and between 6 and 7 inches in length. The anterior portion of the animal which projects from the shell, comprising the cephalic and nuchal regions, with the jaws, organs of sense, motion, and adhesion, is tough and muscular. The posterior portion of the body is covered and protected by the shell, and consequently the body wall is here so thin that the viscera can easily be distinguished through it. The part of the body contained within the shell conforms exactly to the latter. In the middle dorsal region the body is deeply hollowed to receive the involution of the shell. All other portions of the body within the shell are smoothly and evenly convex. The anterior part of the body is covered by the large triangular hood. At the sides and ventrally are the numerous digital tentacles, the sheaths of which, fused to each other and the hood, form a solid wall around the mouth parts, to which the name cephalic sheath has been given. Within the cephalic sheath are the projecting parrot-like mandibles, surrounded by several groups of smaller tentacles. Beneath is the large muscular funnel, the crura of which pass upward upon the sides of the body just back of the bases of the tentacles to the upper edges of the body, where they are joined by the crescentic ridge extending across the back of the hood. (Fig. 2, CR.) In the angle between the projecting posterior corners of the hood, the back of the cephalic sheath and the crura of the funnel, are the large round eyes (E). Two tentacles, the pre- and post-oculars (Fig. 1, O’, O”), spring from close to the base of each eye, while just beneath each eye is a small projecting pyramidal organ supposed to have an olfactory function. The mantle fold projects freely entirely around the body. The edge of the mantle is attached along the edge of the shell, but from the umbilicus of the shell upward it extends as a convex fold covering the dark portion of the involution of the shell. The mantle cavity is shallow dor- sally, while very deep and capacious ventrally. The organs of the pallial complex are all within the ventral portion of the mantle cavity. (Fig. 3.) The four gills, the renal, pericardial, and anal orifices, and certain papillae sometimes spoken of as osphradia, are borne by the mantle. In adult females the inner side of the mantle also bears a large bilateral nidamental gland. (Fig. +, N.) The reproductive orifices are situated upon the body wall near the origin of the mantle. The mantle is continuous posteriorly with the thin and transparent wall of the visceral portion of the body. The body wall is produced from the end of the body as a slender tube, the siphuncle, which extends within the siphon of the shell to its very end. (Fig. 1, fig. 2.) At the sides and above the middle of the body are seen the crescentic areas of attachment of the strong shell muscles by which the body is held to the shell. (Fig. 1,SM.) Beside these areas of attachment, the wall of MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 106 9d ro) DAd —~ ——S —— AO 107 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ‘apyurum yo uorjwod [eayuaa “TW AL BAB) BUDA “CY A “met aoddn ‘py ‘ansuoy “YL, *VUITUBST| augers ayy Aq LavAo ayy tHoay popuodsns “ToRUIOys “YS ‘apunyqdis ‘4 -oaod [Buad ‘OY ‘snsvydosa oy} JO JUSMAITOIUTIOD OY} SB IB] SB onsu0} ay] dopun paBMyorq spus}xo ovs AvpUpvl oy} +B[NpwA 7 juowmesry [BtoostA-orped “TA d “uoTpsues [RadostA-orme[d “4 Ad ‘snpnomyuosord ‘A -eyyided jeuvoid ‘qq -oaod [etpavowted ‘Od -ounsstumuio09 [eped ‘Hq “motes Jo ouR oY} UT aq 07 PRIpett ATJYSTS poaow uooq oAvy syed eso, ‘OBS [BUEL oY} UL osupuedde yeuet oy} st oysoddo ‘pues jerpavorted coneyuR “DH Aad “MOTH JO WOTSTATP [wrprvowtod “aq ‘sso001d yendurjaad sorseysod ‘4 ‘ssoooad pensurpead 1oeyue ‘4 *£IBAO SAO “puvyys [RpWAUIBpTU 4) Ny ‘OPOSDLUL LBNGIPUBUE “WAY “MBE LOMOT {PTT TOATL “T “8qO] [BIGRl LOW9 I ITAL ‘ueaserp omy yo ouryd ay} OFUT yYSNoId -oUlsozUT aI “pooy “OF ourey “AV TY “quay ‘ET “UOTqoaS JO aurd oy) JO Sopls otf} OF TT S[[I5 OUg JO SasBq ayy =[[L9 9) ‘jouUNy JO BABA ‘ALT ‘jauuny Jo sospa surddevjs9ao “yy ‘oqjuBur yo uoTod [esxop ‘Wd oroydozeutseds oy AATO00" YOU SPO} ey Suruwoq yreys oreydoo Jo uortod yesjaos ‘Sp ‘our, poyqop ayy Aq poyBorpUr ST mANTPEyyIda oOMMO[aH) OYZ + TAO FO WOIBTATP yeyues ‘10; “MOTLBUBS [BALGaIed “() “pooy JO Youq UO ploy oyueEdse10 “YO ‘aneytyaRo ‘fy ‘snue ‘W ‘SOTILAVN LO NOLLOUS TVNIGALIDNOT OILVANVADVId— ft PM ixay 108 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. the body is attached to the shell along three aponeurotic bands, two ventral and one dorsal, which extend between the ends of the areas of attachment of the shell muscles. (Fig. 1.) The division of the body of the Nautilus into cephalic, nuchal, and visceral regions is not as distinct as it is in many dibranchiates. At times it proves convenient to recognize such divisions, although they are entirely without morphological importance. For this reason we may consider the cephalic region to be that which bears the tentacles, buccal mass, andeyes. A section through the body just back of the eyes would also pass just back of the central nervous system. The nuchal region is that of less girth, which extends between the posterior edges of the cephalic sheath and the attachment of the mantle. Accordingly, this bears the funnel and its crura, the reproductive orifices, and the mantle. The visceral region comprises the remaining posterior portion of the body, the wall of which we have already noted as thin and semitransparent. THE TENTACLES. A.—DiciraL TENTACLES. For the purposes of description each tentacle will be considered to consist of two parts—a cirrus, which is the active part of the organ, and a sheath which forms a protection for the cirrus. The sheath of certain tentacles is lacking (or undifferentiated), the cirrus, never nor- mally. In this application of the terms we need not take into account the probable morphological importance of the sheath. The digital tentacles include those tentacles which form the cephalic sheath and hood, Each is composed of two parts—a retractile (or extensible) adhesive cirrus, and a tough, thick-walled, more or less rigid sheath into which the cirrus may be entirely withdrawn. (Fig. 1, C; Fig. 49; Fig. 50.) This is the essential structure of not alone the digital tentacles, but all the tentacles with which a Nautilus is so generously supplied. Whatever differences there are, they are modifications of this plan. The digital tentacles are symmetrically arranged upon each side of the head, according to the diagram presented in text-figure 2, CS, p. 116. A careful examination of more than fifty specimens has led me to make this statement in the face of other statements denying any regularity of arrangement of these tentacles. Whether each individual tentacle, as determined by the inner- vation, always occupies the same identical position is more than I can assert, because of the extreme difficulty of satisfactorily following the nerve to each tentacle. However this may be, the arrangement of the tentacles follows a definite plan from which variations were found in only five specimens out of fifty-one examined at one time. * Except in one case the variation occurred upon one side only. I see no especial morphological importance to be attached to this arrange- ment; nevertheless, the fact is interesting and its knowledge may sometime be helpful when the development of Nautilus comes to be studied. As has already been mentioned, the cephalic sheath is formed by the fusion of the sheaths of the individual digital tentacles. The hood, which forms the entire dorsal part of the cephalic sheath, is itself composed of the enormously developed sheaths of two tentacles. (Fig. 1, Ho; Fig. 2, Ho.A.) The hood is roughly triangular in shape. It is thickest in its middle posterior part, sloping from here to thin edges anteriorly and laterally. It presents three superficial fasciv (Fig. 2); a dorsal about an inch in width sloping downward and forward to the anterior edge, and two lateral which slope from the middle fascia to the lateral edges. The dorsal fascia main- tains an equal width throughout its length—this varying in different specimens between 18 and 25 millimeters. Accordingly the anterior edge of the hood is approximately straight and not pointed. The lateral fascise, however, are widest opposite the posterior end of the mid- dle fascia, gradually narrowing to a point anteriorly, and to a blunt rounded extremity pos- teriorly which overlies the umbilicus of the shell. The posterior surface of the hood is pressed closely against the involution of the shell, and following its shape is deeply concave. The postero- *The tentacles of a dozen other specimens since examined have conformed to the same plan, MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 109 lateral corners lying against the umbilici of the shell are sometimes spoken of as the auricles of the hood. (Fig. 2, Ho.A.) In most specimens a slight groove runs along the middle of the dorsal fascia of the hood, although it is frequently absent. Scattered more or less evenly over the surface of the hood are numerous small papille. The possibility of these possessing a tactile function is immediately suggested, but my material shows no structure to confirm it. The papille are differently distributed upon different Nautili, in some being most thickly placed upon the median portion of the hood, in others upon the lateral parts. But comparing one specimen with another, the papille may be said to be evenly distrib- uted over the entire surface. Tn the anterior edge of the hood are two small openings leading into deep cavities, in each of which is a cirrus exactly similar to the cirri of the neighboring tentacles. (Fig. 2, Ho.C.) The presence of the cirri, the innervation and the anatomical relations of the hood, and the fact that the neighboring tentacles are sometimes closely fused with it leave no doubt that the hood is composed of two tentacles, the sheaths of which have become much enlarged and closely fused. It seems probable that the hood of the Nautilus, aside from its other uses, serves to protect the animal when withdrawn into its shell in much the same way as the operculum of a Gastropod protects its owner. It is noticeable how closely the hood of a strongly contracted Nautilus fits the opening of the shell. A cleft of varying depth existed in the middle of the anterior edge of the hood of several specimens in line with the median groove before mentioned. This may be an indication of an originally less completely fused condition of the hood tentacles. Below the hood are eighteen digital tentacles upon each side. Including the tentacles forming the hood there are thus nineteen upon each side, a number from which I found no yaria- tions in any of sixty-six specimens. But that variations in the number do occur is proved by the fact that Rump and Owen each counted twenty tentacles upon a side, while VALENCIENNES found only eighteen upon a side in his specimen. In another specimen Owen found only seven- teen tentacles upon one side, while the number was normal upon the opposite side. The sheaths of the digital tentacles are fused to each other except for a distance of about half an inch at their tips. The exterior of the cephalic sheath is made rough by the projecting angles of the tentacle sheaths, and by this means the course of the individual sheaths can be followed to a certain degree. The internal surface, on the other hand, is perfectly smooth except at one point. The exception is possessed by the female only. Upon the outside of the cephalic sheath are seen four tentacles which are so much smaller than the others that they do not begin to reach the anterior edge of the sheath. The tentacle next the hood on each side possesses a much larger sheath than the remaining lateral tentacles, the increase in size being especially expressed in breadth. The sheath is considerably flattened and overlaps the next lower tentacle sheath as it is itself overlapped by the edge of the hood. It is usually fused along nearly its entire length to the ventral side of the hood, leaving a crease where the edge of the hood projects. (Fig. 1; Fig. 2, DT’.) Its outer surface bears papille like those upon the hood. Normally the tip of the sheath is entirely free, but occasionally its sheath and the hood are so closely fused that no line of demarcation can be observed, the tips of the sheaths being included in the fusion. Rarely other more lateral tentacles may be included in this close fusion, so that the area of the hood may be considerably increased. The remaining tentacles present no differences beyond those of size and shape which we may expect to find. The tips of the sheaths where their shape is unaffected by fusion are roughly triangular or quadrangular. Usually one of the angles is turned outward, and this may be continued as a distinct ridge nearly or quite to the posterior edge of the cephalic sheath. At the sides of the head the posterior part of the cephalic sheath falls away abruptly to the level of the nuchal region. (Fig. 1.) These posterior faces are quite smooth. From the hood they slope first down and back, then, from the level of the lower edge of the eye, they slope down and forward. The faces become narrower as they pass downward and gradually disappear upon 110 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. the ventral surface of the cephalic sheath. The eyes are situated partly within the angles between the auricles of the hood and the upper portions of the just described posterior faces of the cephalic sheath. In the ventral surface of the cephalic sheath is a broad and deep channel, into which fits the dorsal part of the funnel. (Text-fig. 2; Pl. 3, Fig. 3.) The anterior edge of the sheath, in line with the channel, is deeply notched, so that ventrally the tentacles of the two sides are widely separated. (Figs. 24 and 25.) Partly surrounding and extending back from the edges of the ventral notch in the cephalic sheath of the female is the exception previously noted to the complete smoothness of the inner surface of the cephalic sheath. (Figs. 24 and 25.) We see here a large number of low, narrow, glandular lamelle extending parallel to each other from side to side of the area. The lamelle of the anterior half of the organ frequently radiate from centers at each side of the notch in the sheath. Consequently, while their median portions extend trans- versely to the axis of the body, the lateral portions turn more or less sharply forward. The posterior lamellee do not reach the centers referred to, and so the forward bend at the sides becomes less and less pronounced as the back of the area is approached. Finally the most poste- rior lamelle are almost straight. Considerable differences exist in the shape of this area in different specimens. The one which I have described and figured in Fig. 24 seems to be quite rare, although for a considerable time I thought it to be the normal shape. Instead, the lamelle rarely meet at such centers as I have figured. The differences in the descriptions of various authors suggest that practically the only constant feature may be the presence of numerous lamelle, while their arrangement is capable of a high degree of variability. Frequently the area is nearly or quite separated into two portions by a median furrow. VALENCIENNES and LANKESTER refer to the organ as a paired structure. Owen describes it as consisting of ** two clusters of soft conical papillee, and on each side of these a group of lamine disposed longitudinally ”. As noted, the organ, as it may fairly be called, exists in the female only. Slight folds of the skin are often found in the same region of the male, but they are evidently adventitious, resulting from contraction, and do not in any way represent a structure similar to the one possessed by the female. The lamelle of the female form an organ for the retention of the spermatophore. In the case figured (Fig. 25) the spermatophore is arranged with unusual symmetry. In no other instance was it so nicely coiled as in this, though it was always spread out upon the surface of the lamelle so that few coils overlapped. The coils of the spermatophore were in all cases so firmly glued to the lamelle that it was impossible to remove them without breaking either lamellee or spermatophore. Kerr mentions that in his specimen the spermatophore was partly embedded in the coagulated secretion of the lamelle. The secretion has not been so noticeable in my own specimens, being only suflicient to hold the spermatophores, but that very tightly. Having considered the digital tentacles as a complex, the cephalic sheath, let us now consider their individual structure. It has been noticed that each tentacle comprises two parts, namely, a slender retractile cirrus and a tough sheath within which the cirrus may be entirely withdrawn. The completely extended cirri are often fully twice the length of the sheaths. They are supple and slender, tapering slightly to a bluntly rounded point. Average dimensions of the larger cirri would be 10 centimeters in length by + millimeters in diameter. Each cirrus presents throughout its length, except the basal portion, a series of narrow annular grooves and ridges. (Fig. 50.) These vary in number according to the length of the cirrus. Upon a cirrus of ordinary length there are 50 to 60 ridges. The cirri are ordinarily three sided in the portion which is commonly extended outside the sheath, the broadest and flattest side being turned inward toward the mouth. Exceptional cirri which are round are quite common, and in any case the outer angle of the cirrus is much rounded, and the portion which remains inside the sheath is always nearly round, being flattened only slightly upon the inner side. Wi.ry states that the outer sides are deep brown in color, while the inner side is of a pale neutral tint. A MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. taal usual, but not a constant, feature is a shallow longitudinal groove occupying the middle of the inner face of the cirrus. (Fig. 49.) The annular grooves are much deeper upon the inner side than upon the outer sides, and as a consequence the alternating ridges are also much more prominent upon the inner side. (Fig. 50.) To use a comparison, the cirri are somewhat like high piles of thin, flat disks, fastened together through their centers. This comparison, however, applies closely to the terminal third or half of the cirrus only. Upon the proximal part, which is always retained within the sheath, the annular grooves quickly disappear on the outer surfaces. The grooves persist on the inner side, eradually becoming fainter and fainter, until within a couple of centimeters of the proximal end of the cirrus. The proximal end of the cirrus is usually perfectly round and perfectly smooth; it tapers slightly to the base, which has about half the greatest diameter of the cirrus. The terminal disks are broken off with great ease; the query arises if regeneration of some sort does not take place. The inner projecting part of each disk forms an adhesive organ, the structure of which will presently be described in detail. The tissues of the cirrus are continuous at its base with the tissues of its sheath. The sheaths of the larger tentacles have a depth of about 6 centimeters. The epithelium extends from the surface of the cirrus upon the inner surface of its sheath, and over the margin of the latter upon the surface of the body. The free portion of each sheath is usually angular and slightly tapering. At its blunt extremity is a round, oval, or slit-like opening, through which the cirrus projects. The cavity of the sheath frequently extends to near the cephalic ganglia— much farther, therefore, than there is any external indication of the individual sheath. With the exception of those two which form the hood, one sheath is very much like another. The reasons for believing the hood to be composed of the greatly enlarged and closely fused sheaths of two ordinary tentacles have already been given. The tentacle sheaths are composed of a dense felt of large, branched elastic fibres; its inter- stices are occupied by white fibrous connective tissue fibres and nuclei. Small scattering bundles of longitudinal and transverse muscle fibres traverse the sheaths. In places the longitudinal muscles approach a regular arrangement. The amount of muscular tissue is, however, so small that there can be but very little movement of the individual sheaths. The external surtace of the sheath is covered by a columnar epithelium, the cells of which measure 52/4 by 44-8; the cells lining the cavity of the sheath are much lower, being only 244 by 34-6 in their dimen- sions. Both inner and outer epithelia contain very numerous glandular cells. The oval nuclei are situated in the lower half of the cells, but do not all lie in one plane. Large capillaries with endothelial walls are surprisingly numerous in the tissues of the sheath, and here, as elsewhere, the capillaries do not collapse when empty. But the vascular system is not completely closed. The tissues of the sheaths are like a fine mesh work, in the spaces of which the blood flows freely. There is no dermis. The hood presents some modifications of this plan. The cells of the epithelium measure 364 by 44-6. Immediately beneath the epithelium is a dermis formed by a layer of particularly closely woven elastic fibres which, on account of its density, is easily distinguished by the naked eye from the underlying tissue, although it can not be readily dissected away. The dermis is almost entirely destitute of muscular fibres and is penetrated in every direction by great num- bers of vascular lacune. But even in the hood the dermis is not an absolutely constant char- acter. Throughout the hood numbers of capillaries with endothelial walls can be seen. The capillaries are of large caliber and, curiously enough, remain open when empty, so that their cross sections are circular. In the posterior part of the hood many large muscles run in various directions just beneath the dermis. They form a layer which seems to have much to do with the contraction of the posterior portion of the hood. The muscles become smaller and less numer- ous toward the outer side and the deeper portions of the hood. Posteriorly the hood is concave and fits snugly around the involution of the shell. The epithelial cells of this are smaller than those of the upper surface of the hood and of the remain- der of the cephalic sheath, their dimensions being 284 by 34-64. The epithelial cells of this surface as well as those of the upper surface of the hood are loaded with fine granules of a 112 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. brown pigment. In sections the pigment appears as a dark band near the outer ends of the cells, a narrow unpigmented band being outside this, while the pigment granules gradually disappear toward the bases of the cells, ieaving this region also uncolored. These surfaces of the hood bear numereus small pits lined with the pigmented epithelium. Granular cells are exceedingly numerous, especially upon the concave posterior face of the hood. It seems probable that the dark brown, sometimes black, layer of organic matter found upon the involution of the shell is deposited by these cells. The thin crescentic ridge which projects from the posterior face of the hood does not possess a pigmented epithelium and may not play any prominent part in the deposition of the dark layer. The great density of the elastic tissue makes the cephalic sheath exceedingly firm and diffi- cult to penetrate. It must afford a very considerable protection to the Nautilus. A cross section of a cirrus shows a highly muscular organ, usually of triangular outline in its terminal third. (Fig. 49.) Near the center is a large nerve which extends the entire length of the cirrus. (Fig. 50,N.) The nerve is situated toward the inner side of the cirrus, i. e., toward the flattened side turned toward the mouth of the animal. Close to the nerve and upon its inner side is a small strong walled artery (A), and still closer to the inner side of the cirrus is a some- what larger vein (V). The nerve is surrounded by a sheath of connective tissue and muscle fibres (T), while outside this is a mass of longitudinal muscles forming the greater part of the cirrus (LM). The connective tissue and muscle fibres surrounding the nerve are mostly trans- verse to the axis of the cirrus, and they pass outward in such a way as to divide the longitudinal muscles into radiating bundles which appear in cross section like the spokes of a wheel. The radial arrangement is almost lost upon the inner side of the nerve, where the muscle bundles become small and irregularly arranged. The radial longitudinal muscles do not extend to the periphery of the cirrus. They are bounded by a narrow band of oblique muscles (Fig. 51, OM). Outside this is a layer of small bundles of longitudinal muscle fibres (LM.); while outside the latter is a thin layer of circular muscle fibres (CM). The outer muscular layers lose their identity upon the inner side of the cirrus, where transverse muscles predominate. A thin layer of con- nective tissue frequently separates the external circular muscles and the epithelium. The peculiar arrangement of the longitudinal muscles persists for a time after they enter the body wall at the base of the cirrus, but it is then lost as the muscles separate. If, now, we examine the radially arranged longitudinal muscles more carefully we find that ach muscle is composed of a large number of small fasciculi, held in a mesh work of connective tissue into which penetrates an occasional transverse muscle fibre. The fasciculi of the longitu- dinal muscles do not extend straight up and down the cirrus, but have a slightly oblique course upward and inward; i. e., as the muscles pass toward the tip of the cirrus the fasciculi pass from the outer to the inner side of the muscle. (Fig. 50, LM.) The fibres of the fasciculi, however, take a course parallel to the axis of the cirrus and are only rarely oblique to it. The transverse muscle fibres radiate in all directions from about the nerve, passing between the longitudinal muscles and penetrating the outer circular layer. (Fig. 51.) The fibres are gath- ered into strands, few of which, however, radiate directly outward from the nerve, though at first sight they may seem to do so. Most pass in an hyperbolic curve from between two longi- tudinal muscles to between two others about 90 degrees away. Under this arrangement, when the transverse muscles contract, the outer portions of the cirrus alone are compressed and the nerve is not disturbed. After repeated examinations I am convinced that these are actually mus- cle fibres and not some form of connective tissue which, in the invertebrates, is often so hard to distinguish from muscle tissue. There is also considerable connective tissue in the transverse strands of the cirrus. The fibres of the longitudinal muscles of the cirri are unstriated, smooth, slender, and exceedingly long (400 /« to 600 4), and tapering gradually to pointed ends. An oval nucleus lies at the side of the cell near its middle. There is very little elastic connective tissue in the cirrus. The retraction of the cirrus is accomplished by the longitudinal muscles; the elongation by MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 113 the circular, oblique, and transverse muscles. Their peculiar arrangement enables the cirrus to elongate or shorten without any undue pressure upon the central nerve. The arrangement of the cirrus muscles is very similar to that in the arms of the Octopoda and Decapoda. In these also there is a large, nearly central nerve, surrounded by a mass of connective tissue and trans- verse muscle fibres. Around this are the longitudinal muscles, which are also arranged radially. But instead of forming a complete circle, as in the cirri of Nautilus, the longitudinal muscles form two to four separate masses. In its essential features, however, the arrangement is remarkably similar in both the Di- and Tetra-branchiata. It has been mentioned that between the annular grooves of the cirrus are comparatively wide projecting ridges, which show well in a longitudinal section of a cirrus. (Fig. 50.) The ridges are annular, extending completely around the cirrus. The inner portion of each annular ridge projects considerably more than the outer portions and forms an organ of adhesion. Into this projecting portion great numbers of muscle fibres extend nearly perpendicular to the inner sur- face. (Figs. 50and 51.) The arrangement of the muscles in this region is very peculiar. Naturally there are almost no longitudinal fibres present. As the transverse muscles issue from between the inner longitudinal muscles they seem to branch to form an extensive brush, the outer ends of which are applied to the basement membrane. The muscle fibres are not branched, but are so attached to one another (like the straws of a broom to the handle) as to form a central strand which passes between the longitudinal muscles. (Fig. 51, RM.) This strand can be traced in an arc, as has been described for other transverse muscle fibres, across a portion of the cirrus till it passes outward between longitudinal muscles. Apparently the central strand serves as a sort of tendon to the radiating fibres of the inner portion of the annular ridge. These radiating fibres are short and thick, and quite unlike those in the other portions of the cirrus. As each strand forming the so-called tendon runs to an opposite portion of the cirrus the contraction of all these can scarcely take place without causing some contraction of the cirrus in a transverse direction, i. e., a lengthening of the cirrus. Possibly many of the arcuate trans- verse fibres share in this action. As the contraction of the radiating fibres within the inner portion of the ridge would pull the inner face of this latter inward, a sucker is thus formed. If these suckers were applied to any object the effect of the contraction of the transverse fibres in the body of the cirrus would be not to lengthen the latter, but to increase its rigidity, and thus increase the mechanical effi- ciency of the suckers along it. Any one such sucker would possess but little holding power, but thirty or more suckers upon each of thirty or more cirri must be able to hold very strongly. Witey says that ‘most of the tentacular appendages of nautilus have essentially an adhe- sive function, to which is related a prehensile function. They are employed for seizing hold of food and for attachment to surfaces. Attachment is effected by the definite suctorial ridges upon their lower and inner surfaces. When attached by its tentacles, nautilus holds on with considerable tenacity, and sometimes in forcibly detaching it some of the tentacles break off and remain fixed to the surface of attachment.” In Fig. 1, pl. 11, Q. J. M. S. 40, WILEY repre- sents a Nautilus holding to a glass vessel. In considering the remarkable holding power of cephalopod suckers we must remember that attachment is effected under water, so that a perfect vacuum is possible. Another condition must affect the deep-sea forms like Nautilus much more, namely, that they are under a pressure of 20 to 80-atmospheres, where any vacuum attachment would be immensely more powerful than at the surface. The nerve of the cirrus extends throughout its length, remaining of the same size nearly to the end. It tapers slightly here and ends abruptly immediately beneath the epithelium of the tip of the cirrus. (Fig. 50.) Ganglion cells are found at the periphery of the nerve as far as it runs in the cirrus. (Fig. 71.) But in regions corresponding to the annular ridges aggregations of ganglion cells are found which form annular enlargements or ganglia upon the nerve. There is a ganglion for each and every annulus. Numerous small nerves arise from these ganglia and pass to the external parts of the cirrus. Branches to the inner portions are especially numerous. 114 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. The nerves to the digital tentacles arise singly, as a rule, from the outer edges and lower side of the pedal ganglia. (Fig. 41, 9.) Only the nerves to a few of the more dorsal tentacles arise from a common nerve. (Fig. 41, 10.) The hood receives branches from several nerves. A small artery with thick elastic walls is found close to the inner side of the nerve. (Fig. 51, A.). Just outside this is a much larger vein. (Fig. 51,V.) Both vessels are elliptical in cross section. This position of the artery and vein is so characteristic that even in extremely modified cirri, such as those of the spadix, the inner side of the cirrus can be determined at once in sections by the position of the vessels. Between the epithelium of the cirrus and the circular muscle are numerous, very large, capillaries with endothelial walls. Closed capillaries are occasionally, but rarely, found in the muscular and nervous tissue. Here the circulation takes place through minute fissures in the tissues. Immediately behind the cerebral ganglion the dorsal aorta divides into two branches—the innominate arteries, from which arise branches to the eyes, buccal mass, labial tentacles, funnel, shell muscles, and cephalic sheath (Text-fig. 10). The posterior portion of the hood is supplied by small arteries arising directly from the innominates (10). The main branches of the innomi- nates run forward and downward upon each side, giving off branches to the individual digital tentacles (5, 4). The veins of the cephalic sheath unite in common yeins which penetrate the cartilage and enter the anterior end of the vena cava. The epithelium of the cirri forms a feature of exceeding interest. It consists of a single layer of slender columnar cells. The epithelium upon the outer sides is of the ordinary type and contains great numbers of goblet cells. These cells are 40/¢ in height by 4 in diameter. In the bottoms of the annular grooves the cells are very much shorter, often almost cubical. But the epithelium of the inner surface of the ridges is very peculiar. A longitudinal section of a cirrus (Figs. 50 and 72) shows that the upper surface of the projecting portion of rach ridge is horizontal and makes a sharp angle with the inner surface, while there is a gradual bend from the inner to the lower surface. The epithelial cells of the vertical inner surface are exceedingly slender, having a height of 1084 and a width of 2-44. Their width has been exag- gerated in the figures of the single cells shown at the left of Fig. 72, as well as in the main portion of Fig. 72, for convenience in representation. The epithelial cells of the upper surface of the projecting portion of the ridge are only about one-eighth as high and much wider, beside being of a totally different character. The change from one kind of cells to the other takes place quite abruptly at the sharp angle of the ridge. The change in length and character of cells is much more gradual where the epithelium passes from the inner to the lower surface. The relations and characters of these cells are shown as well as my limited ability as an artist allows in Fig. 72, which was drawn from a section stained with borax carmine and Lyons blue; the colors of the stain have been copied faithfully. The epithelium of the upper surface contains many mucous cells the secretion of which remained unstained with either stain, excepting the portion extruded from the cells and certain small granules which stained red. Mucous cells are occasionally found in the depth of the groove, but none, of this character at least, are found upon the inner surface of the ridge. The nuclei of the slender cells upon the inner face of the ridge are situated very close to the bases of the cells. From the nucleus out almost every cell contains a large number of granules which stain a brilliant red. Sometimes the granules are arranged in a single row extending from the nucleus to the free end of the cell. Sometimes they form a dense accumulation almost filling the body of the cell. A very few scattered granules were sometimes found in the base of the cell beneath the nucleus, but never in any numbers or regularly arranged as they usually were upon the outer side of the nucleus. The granules seem to be some sort of a secretory product, but this is evidently of a different chemical nature, as well as physical, from that formed by the cells of the upper surface of the ridge or of the entire outer sides of the cirrus. Possibly its formation is connected with the function of adhesion belonging to these portions of the cirrus. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 1S Beneath the epithelium just described is a thick basement membrane. This is exceedingly uneven, being fullof small pits. The unevennesses of the basement membrane, however, are not copied by the surface of the epithelium. Over the remainder of the cirrus the basement membrane is very thin. The transition from thick to thin basement membrane is as sudden and marked as the transition from high to low epithelial cells, and occurs at the same place. (Fig. 72.) Many of the slender cells of the inner surface of the ridge taper to a fine thread-like base, which often seems to penetrate the basement membrane and to be continued a short distance toward the center of the cirrus as a slender fibre, but it is not possible to be sure of this because of the unevennesses of the basement membrane. What appears to be a fibre penetrating the membrane may be only the slender basal portion of a cell entering one of the pits of the membrane. We can not help but suspect from their shape, position, and structure that these cells are sensory as well as secretory, but the determination of this question will require specially prepared material. Here, as in other places where the histology of Nautilus is described, descriptions of the tissues are given as they have been found under certain (rather unfavorable) conditions, and no attempt is made to insist upon any doubtful interpretations. Variations in the shape and structure of the tentacles are quite common and take place in four directions, as far as my observation extends. 1. The free ends of the sheaths may be more or less fused; fusion may occur between any two sheaths, but is most usual among those nearest the hood. 2. The free portion of the sheath is sometimes split into two halves, leaving the cirrus projecting between them. This may be the result of injuries received by the animal early in life, but no trace of any injury is shown by any other part and the innermost digital tentacles are always the ones to be affected; from their position we should expect these tentacles to be rather less exposed to injuries than any others. 3. The opening through which the cirrus projects from the sheath may be displaced. Usually the displacement is toward the inner side and the opening is found a few millimeters below the tip of the sheath. But it may be at the very base of the sheath, which then projects in the usual manner, but with closed tip, while the greater portion of the cirrus lies outside the sheath. Less frequently, and only among the dorsal tentacles, the openings are upon the outer side of the sheath. In one specimen one of the cirri of the hood extended from its sheath 10 milli- meters back from the edge of the hood. The hood-cirrus of the other side was normal, while the cirri of the two neighboring tentacles both projected from the sides of their sheaths several millimeters back from their tips. 4. The cirrus may be entirely absent and the sheath closed. This occurred in but one specimen. Where the cirrus of the left side of the hood should have projected, only a nipple- like projection of the integument was seen. Upon slitting the hood back of this projection the cavity of the sheath was found empty, without the least trace of a cirrus, and not extending the usual distance into the hood. The more common variations of the tentacles were those of fusion of the sheaths with one another. The general tendency, in fact, seems to be toward more complete fusion and increasing solidity of the cephalic sheath. B.—InnER TENTACLES OF THE FEMALE. If now we open the cephalic sheath or cut it away we see that the mouth parts of both male and female Nautili are surrounded by still other groups of tentacles. We see, further, that these groups are evidently more specialized than the digital tentacles, and that the groups are not alike in male and female, either in number, shape, or position, while their specialization is of a higher degree in the male than in the female. It is therefore impracticable to attempt a parallel description of the inner tentacles of the two sexes. The conditions are more simple in the femate, so I shall attempt their description first. The tentacles about the mouth parts are designated by the general name ** labial tentacles.” Vol. 8—No. 5——2 116 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. Two groups situated upon either side of the buccal cone, and nearly meeting dorsally, are the superior labial tentacles. (Fig. 5, SLL; Text-fig. 2, SLL.) Two other groups, situated below the buccal cone but wrapping around it laterally, are the inferior labial tentacles. (Fig. 5, L; Text-fig. 2, ILL.) The superior labial tentacles project from two broad, flat, thin lobes which arise from the base of the inner side of the cephalic sheath. The lobes are about 3 centimeters broad and 2 centimeters high. From the ends of the lobes low ridges are continued; dorsally to unite the two, ventrally to end above the funnel near the innermost digital tentacle of each side. (Text- fig. 2.) One might say that these two lobes are only local elevations of a single ridge which nearly surrounds the mouth parts. The upper edge of each lobe is subdivided into a number of more or less separate processes. The tip of each process is free for from 6 to 10 millimeters, while grooves upon both surfaces of the lobe indicate a division for some distance farther back. At the tip of each process is an opening leading into a cavity 14 to 2 centimeters TEXT-FIG. 2.—Diagram of the arrangement of the tentacles of the female nautilus, viewing them from the front. B, buccal mass. CS, cephalic sheath, composed of the fused sheaths of the digital tentacles, ILL, inferior labial lobe. SLL, superior labial lobe. 1,2,3,4,a series of four small digital tentacles upon the outer side of the cephalic sheath, deep; each projection is the free end of the sheath of the cirrus which projects through its opening. Thus the superior labial tentacles have the same principal structures as the digital tentacles. The number of tentacles in the superior labial group is very variable within certain limits. The most ordinary number is twelve in each group; as few as ten, or as many as fourteen are quite common. Rumpr (1805) counted sixteen in each group. The number is usually, but not necessarily, the same in both groups of one individual. I have not, however, found a difference of more than one. The arrangement of the tentacles seems to be constant. As is shown in the diagram (Text- fig. 2) there is an inner row of nine, and, at about the middle of this, an outer row of three. The variable tentacles seem to be at the ends of the longer row, the shorter row having always been found to be normal. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 117 The cirri of the labial tentacles are, of course, shorter and more slender, but their structure and shape are the same as of the digital tentacles. The structure of the inferior labial lobe is more complicated. I have retained OwkEn’s designations of superior and inferior instead of the ones suggested by VAN DER Hoeven, external and internal, for these lobes because the former names indicate better their actual positions. I have already spoken of two inferior groups of labial tentacles. Two groups there are, but they are borne upon a single lobe, the inferior labial lobe. The inferior labial lobe (Fig. 5, L; fig. 26) arises immediately below the buceal cone as a process about 24 centimeters broad and 8 millimeters thick. About 24 centimeters from its base the process is split into two symmetrical portions. Each portion widens out like a fan and bears a single row of tentacles along its edge. (Text-fig. 2, ILL.) Each of these parts wraps itself about the buccal cone internal to the superior labial lobes. The inner surface of each is concave, the outer surface convex. Sheaths and cirri of the inferior labial groups are like those already described for the superior labial tentacles, except that the sheaths do not project freely. The middle tentacles of each inferior group are the longest; those at the outer end of the row are only slightly shorter, but the inner tentacles decrease rapidly and greatly in size. A’ progressive reduction in the development of the sheaths is also noticeable among the innermost tentacles. The innermost tentacle is frequently a mere papilla 2 or 3 millimeters in height. The number of tentacles in each inferior labial group usually varies between ten and fourteen. The number upon the opposite divisions of the same lobe frequently differs by one or two. Van DER Horven reports fourteen upon the left and sixteen upon the right side. At the junction of the outer portions of the lobe, upon its inner side, is an oval or polygonal organ composed of sixteen to twenty closely folded thin triangular lamellae, the widest portion or base of the organ being directed posteriorly. (Fig. 5, L; Fig. 20; Text-fig. 2, ILL.) Usually sixteen lamellee compose the organ, which OwEN supposed to be the olfactory organ of Nautilus. The lamellz are symmetrically disposed with respect to the median line of the body. Occa- sionally there is a difference of one in the number of lamelle of the two halves of the organ. The organ represented in Fig. 20 was more expanded than most, so shows the relative arrangement and form of the lamelle better than is usually the case. This organ measured 12 millimeters in breadth and 9 in length. The triangular lamelle are attached to the labial lobe by one edge, the point opposite then projecting upward and inward. The line of attachment of each of the median lamell is parallel to the axis of the body, while the outer lamelle are attached at acute angles to the axis. The outer lamella of each side usually lies somewhat above the others, over- lapping them and lying in the continuation of the rows of tentacles upon the outer parts of the labial lobe. A ridge across the open back of the organ connects the two outer lamelle. Each lamella is distinctly and closely grooved upon its outer side, the grooves reminding one of those upon the cirri. Less numerous, distinct, and regular grooves are seen upon the inner sides of the lamelle. A large nerve runs through the center of each lamella to its tip. The nerve possesses an outer layer of ganglion cells which are evenly distributed upon its surface and not grouped in ganglionic masses as they are upon the nerve of a cirrus. Both surfaces of the lamelle are deeply pitted, and all portions are covered with a highly glandular epithelium. ‘The musculature of a lamella has essentially the same arrangement as that of a cirrus. In consequence of the flattened form of the lamellw their longitudinal muscles extend outward to the edges upon either side of the nerve. The transverse fibers, which are radially arranged about the nerve in the cirri, here, therefore, pass directly across the thin lamelle between the bundles of longitudinal fibres. External to the latter are circular muscle fibres. In the farthest depths of the fissure between each two lamelle is a small opening leading into a sunken organ which I do not hesitate to call sensory. These organs ordinarily consist of two parts: 1, a tubular neck opening outwardly as has just been mentioned, and opening inwardly into 2, a (comparatively) large cavity which extends in the solid tissue of the labial lobe at right angles to the surfaces of the lamelle. (Text-fig. 3, G.) The whole structure reminds one strongly of a diminutive tunnel driven in both directions 118 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. from its shaft. The tunnel is round in cross section, and 1s a rule the shaft is near its center. A section of the organ through the middle of its shaft therefore is flask-shaped, the neck (shaft) being slightly bulged at its center. The shaft may, however, be at one end of the tunnel. Shaft and tunnel are lined throughout with a peculiar epithelium. The cells are extraordinarily slen- der, almost like threads in their proportions, and the free end of each is prolonged into a sensory spike, the multitude of which causes the surface of the tunnel and shaft to appear ciliated. A very slender nucleus is situated in the basal third of each cell. None of the cells lining the cavity are glandular. The length of the cells varies greatly in different cavities, as well as in different regions of the same cavity. This peculiar epithelium may extend outward from the mouth of the shaft for a little distance into the fissure between the lamelle. I have not observed any special nerves going to these organs, but as they lie close to the large nerves of the lamelle better material may reveal the innervation. There seems to me to be but little doubt that these cavi- ties are sensory organs of a simple type, and but. little more doubt that their func- tion is olfactory as was as- sumed by OwEN and others for for the group of lamelle as a whole. I find, however, no sensory structures upon the lamelle, nor any indication of these latter possessing any spe- cial sensory function. The sensory organs situ- ated between the outer three or four lamelle may be less developed than those between the inner lamelle. The shaft may be shorter; the tunnel short, or little more than a spherical pocket. In two cases the only indications of the sense organs were small hemispherical projections be- Texwric. #/—Camera) lucida outline ofa) gestion of the lameliatedvoreanl off teuinterone (UNieeMiun e] bases of the lamellee eee GTN Enel Gone a 13. covered by the sensory epi- thelium. These were the two outer organs of one side. But there was no gradual transition from this to the more complicated and apparently more typical form of organ. The muscles of the tentacles pass into the labial lobe as in other cases already described, interlacing here with the numerous intrinsic muscles. The inferior labial lobe is a strongly muscular and evidently contractile organ in both its divided and undivided portions. A rather complicated system of muscles extends from its base to the surrounding regions of the cephalic sheath, providing for the motion of the lobe in all directions. The inner side of the cephalic sheath and all the organs within it, labial lobes and buccal cone, are covered with what may fairly be called a skin. This may easily be removed from their surfaces, leaving the muscular bases of the organs bare. It consists of a single layer of columnar epithelial cells similar to those upon the outer surface of the cephalic sheath, resting upon a thick connective tissue dermis. The dermis tissue is somewhat fibrous, but reminds one strongly of MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 119 embryonic gelatinous tissue. Probably better preserved material would show more structure than I have been able to discover. When the skin has been removed from the labial lobes their muscles come into view. The muscle fibres of the superior labial lobes pass into the tissues of the cephalic sheath without forming any distinct muscles. But in regard to the inferior labial lobe the case is very different. A longitudinal median muscle, the dorsal median retractor (Fig. 26,5), extends over the dorsal face of the lobe from just back of the lamellated organ to the base of the lobe, where it enters the ventral portion of the cephalic sheath immedately above the funnel. A similar, but much smaller, longitudinal muscle follows a similar median’ course upon the ventral face of the lobe. There remain three pairs of muscles arranged symmetrically at the sides of the lobe. 1 and 1’ (Fig. 26) extend out and back from the sides of the lobe to insertions in the lateral regions of the cephalic sheath immediately below the bases of the superior labial lobes. These appear to be the muscles used in raising the lobe and its tentacles. 2 and 2’ (Fig. 26) originate near the base of the lobe and pass outward from the median line over the base. The outer ends of these muscles are expanded and flattened, and are inserted over the inner faces of the superior labial lobes. This arrangement evidently serves for the approximation of the superior and inferior lobes and their tentacles. The posterior portions of the inner ends of 2 and 2’ separate from the remainder of the muscles and unite with each other above the median muscle 5. The muscles 3, 4, and 3’, 4’, (Fig. 26), the lateral retractor muscles, have their origins in the posterior region of the lobe beneath the inner parts of the muscles 2 and 2’. They pass beneath these latter backward and slightly toward the median line. Arising as single muscles, they separate into two distinct portions. The smaller outer portions pass into the base of the buccal mass behind the inferior buccal retractors, as is shown for similar muscles in the figure of Van DER Horven’sorgan. (Fig. 29.) The larger inner portions pass back to insertions upon the median processes of the cartilage. The base of the lobe is thick and muscular and its tissues extend directly into the ventral portion of the cephalic sheath. The inferior labial lobes are supplied with blood by a branch from each tentacular artery. (Text-fig. 10, pp. 182, 3.) A large nerve leaves each pedal ganglion near the infundibular nerve (Fig. 41, 7), which runs forward and enters the side of the inferior labial lobe. Within the lobe it enlarges into a gan- glion, from which the separate nerves of the tentacles and the lamellx arise. (Fig. 41, 35.) It must be noted that while the inferior labial lobe is bilaterally symmetrical it is not paired as are the superior labial lobes. Young specimens seem to indicate that it is unpaired in its origin. We have still to consider what the relation is between the lamellae upon the median part of the lobe and the tentacles upon either side of the lamelle. Can the two sorts of structures be homologous, or must they be considered as developed separately—one for adhesion and the other for smelling, tasting, or some other function / It has already been noted that as we approach the lamelle the inner cirri of each side, i. e., those nearest the lamelle, rapidly decrease in length. Hand in hand with the decrease in length of the cirri goes a decrease in the depth of their sheaths. Moreover, we often find that the tentacle next to the lamelle is a small, scarcely noticeable papilla. In some cases such a papilla is partly or wholly surrounded by a shallow groove. Further development of papilla and groove would lead to the formation of a cirrus and a sheath, and tentacles sometimes actually illustrate steps in this process. The minute papille, annularly grooved, are supplied with a nerve similar in all respects but length to the nerve of fully developed cirri. On the other hand, the outer lamelle are sometimes small and not much different from the rudimentary tentacles just described. So, if we consider shape alone, it is not at all difficult to imagine that lamelle and tentacles are but differently developed individuals of a single series. 120 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. There are, however, other facts which favor this view. The transverse furrows upon the outer sides of the lamelle are obviously comparable with the grooves upon the cirri. We also note that each lamella possesses a nerve extending throughout its length which has essentially the same structure as the nerve of a cirrus; it has a like complete investment of ganglion cells, although these are not collected into ganglia; beside this, the nerves of the lamelle arise from the same ganglion as the nerves of the cirri, and it is impossible to distinguish the nerves of cirri and lamelle before they arrive at their respective terminations. The nerves of the lamelle are simply the innermost of the series arising from the ganglia. The arrangement of the muscles of the lamelle is according to the same plan as is that of the cirri. We have also noted that the sensory organs at the bases of the outer lamelle have a tendency to be simpler or less developed than those between the inner lamelle. The number of both lamelle and cirri is quite variable, but the number of lamellae does not seem to bear any constant relation to that of the cirri. The entire number of lamelle and cirri borne by the inferior labial lobe is about forty. The facts stated seem to indicate that the lamellated organ is composed of a number of slightly modified labial tentacles, and is not a structure developed upon the labial lobe separately from the tentacles. Furthermore, there are indications that the outer members of the series of lamelle and the inner members of the series of tentacles graduate into each other, possibly being developed in one direction in some individuals and in the opposite direction in other indi- viduals. The inferior labial lobe of a half-grown female showed an interesting condition in the development of the lobe. The superior labial lobes were as well developed, proportionally, as ina mature specimen. The inferior labial lobe, on the contrary, was in a rudimentary condition. It reached only about to the middle of the buccal mass. Each side of the anterior edge of the lobe was produced in a curve; in the center were a number of fine lamelle. The tentacles at the edges of the lobe were very rudimentary, in many cases apparently not yet being differ- entiated into cirrus and sheath. Haswett makes the following statement: ‘‘One of the six or eight female specimens examined by me presents a condition of the median minor tentaculiferous lobe which may, per- haps, have a bearing on the functions of the part. In this specimen, which was a good-sized one and fully developed in other respects, the lobe in question (the group of lamelle) was repre- sented by a rudiment, in which, however, all the parts of the perfected structure were distinctly and symmetrically represented.” C.—InnerR TENTACLES OF THE MALE. The arrangement which we see when we open the cephalic sheath of the male is quite dif- ferent from that which we have observed in the female. The buccal cone occupies the same relative position in both sexes. At each side of and dorsal to the buceal cone of the male is a eroup of tentacles closely resembling the superior labial tentacles of the female. (Fig. 7; Text- tic. 4.) They are borne upon two lobes which are elevations of a ridge of the base of the cephalic sheath nearly encircling the buccal cone. The ridge is very low dorsally and ventrally to the tentacle lobes, which latter rise to a height of from 14 to 3 centimeters. Ventrally the ends of the ridge approach each other like the tips of a horseshoe and end upon the cephalic sheath near the innermost digital tentacle. This ridge obviously corresponds to the similar ridge of the female which bears the superior labial lobes, and we shall also term these tentacle- bearing lobes of the male superior labial lobes. Outside the ventral ends of the ridge bearing the superior tabiai 1obes are two groups of tentacles, one at each side of the head, which do not appear in the female. There are four ten- tacles neach group. (Fig. 7, Sp, ASp; Text-fig. 4,5, AS.) The tentacles of the right-hand group do not differ markedly from the tentacles of the superior labial group. The tentacles of the left- hand group, however, are enormously developed and form a conspicuous organ known as the spadix. The smaller corresponding group of the right side is called the antispadix. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. I Immediately beneath the buccal cone is still another organ which is peculiar to the male. It was discovered by VAN per Horven, and has since been known as VAN DER HorveEn’s organ. It lies in a pocket formed by the ventral portion of the cephalic sheath ventrally, and dorsally by a fold connecting the ends of the horseshoe-shaped ridge which bears the superior labial lobes. (Text-fig. 4, V.) The organ can not be seen until the cephalic sheath has heen opened, so closely does it lie under the buccal mass. Even then the observer can only notice that its anterior end appears to be formed of small lobes and is bilaterally symmetrical. In the diagram (Text-fig. 4, V) it is represented, for the sake of convenience in drawing merely, as projecting at some dis- TEXT-FIG. 4.—Diagram of the arrangement of the tentacles of the male nautilus, yiewing them from in front. AS, antispadix; B, buceal mass; CS, cephalic sheath, composed of the fused sheaths of the digital tentacles; 0’, preocular tentacle; O”, postocular tentacle; S$, spadix; SLL, superior labial lobe; V, Van der’‘Hoeven’s organ. tance from the buccal mass, which it does not actually do. Its shape is roughly outlined by the dotted line. I hope to present sufficient evidence to be convincing that VAN DER HOFVEN’s organ is the homologue of the inferior labial lobes of the female. SUPERIOR LABIAL LOBES. The only considerable difference between the superior labial tentacles of the male and those of the female is in their number. Eight tentacles are usually borne upon each superior labial lobe of the male, while twelve is the usual number upon each of these lobes of the female. Less than eight tentacles may occur upon each lobe of the male, although I have never found more than this number. Two of my specimens presented only six tentacles upon each lobe; one speci- men had six upon one lobe and seven upon the other. The superior labial tentacles of the male are slightly more robust than those of the female; their sheaths are more completely separated in the male than in the female. Two of the tenta- 122 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. cles are more or less crowded to the outside of the row formed by the other six,as is shown in Text-fig. 4,and in Fig. 7,5LL. Aside from these there are no differences between the superior labial lobes and tentacles of the two sexes. Each cirrus possesses a nerve, which springs directly from the pedal ganglion. These nerves leave the edge of the ganglion just dorsally to the nerves of the digital tentacles; being of only about half the size of the latter they are easily distinguished from them, although not so readily traced to their respective cirri. SPADIX AND ANTISPADIX. The spadix and the antispadix are morphologically equivalent organs, although the anti- spadix is simple in all its parts, while the parts of the spadix are highly developed and moditied, and several structures are there developed which are not represented in the antispadix. A previous study of the : antispadix will probably aid in the understanding of the spadix. Before proceeding, we must notice the position of the two organs. The spadix is usually upon the left side of the head and the antispadix upon the right side, but this arrangement may be reversed. Out of forty-seven male Nautili, nine, or 19 per cent, had the spadix upon the right and the antispadix upon the left side. Wuitiry found an even greater proportion of reversals. ‘*Out of thirty-seven males which were examined ad hoc, twenty-three had the spadix upon the left side and fourteen had it wpon the right side” (1896, 1)). This is 37 per cent of the total. One of my specimens possessed a well-developed spadix upon one side and an abnormally developed spadix upon the opposite side. The antispadix is composed of four tentacles similar to those of the superior labial groups, except as they are somewhat larger and longer than the latter. (Fig. 7, A. Sp; Fig. 12.) The tentacies arc arranged in a row, which in the natural position of the animal is dorso-ventral. To distinguish the tentacles I shall number them 1, 2, 3, 4, from above downward, and shall speak of them as the first, second, third, or fourth tentacles. The sheaths of the first, second, and third tentacles are fused as far as their tips, thus forming a narrow, flattened process. It is convenient to speak of the fused sheaths as the sheath of the antispadix. The fourth tentacle is united to the process at the base only. (Fig. 12.) It is situated a little externally to the other tentacles, extending past the third, so that its dorsal edge comes to lie in a groove formed by ¢ projection of the sheath of the antispadix. At the bases of the cirri the muscular tissues of the cirri and their sheaths unite to form a strong, flat sheet of muscle, which lies against the inner side of the cephalic sheath, but entirely separate from it until near the cartilage. Here it unites with the tissues of the esa sheath. The muscular base of the antispadix is entirely separate from the muscular base of the superior labial lobe, although close to it. It is easily seen when the skin between the antispadix and the buccal mass has been cut. Upon the outer surface of the sheath of the antispadix, near its tip and between the first and second cirri, is a small glandular area. (Fig. 12, G.) Its structure will be described with that of a similar area upon the sheath of the spadix. The antispadix projects from a pocket betweea the cephalic sheath and the ridge of the labial lobe and at the ventral end of the lobe. (Fig. 7; Text-fig.4.) The lobe of the antispadix 1s about two centimeters in length from the base of the pocket to the tip of the sheath. As a consequence of the shortening of the rows, the superior labial tentacles are further removed from the ven- tral side of the cephalic sheath in the male than in the female. (Text-figs. 2 and 4.) The low ventral portions of the labial ridge are therefore considerably increased in length in the male. As the spadix increases in size it crowds the superior labial tentacles of this side still farther toward the dorsal side of the head and stretches the ventral portion of the labial ridge. The spadix presents a very different appearance from the antispadix upon the opposite side of the head. (Fig. 7, Sp.; Figs. 13 and 14; Text-fig. 4,8.) It forms a large, very solid organ, five to seven centimeters in length, two to three centimeters in dorsi-ventral measurement, and one MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 123 anda half centimeters in thickness. It remains of about the same width and thickness nearly to the irregu- larly conical end. The tentacles of the spadix have the’ same rela- tive arrangement as those of the antispadix. Each is greatly in- creased in size, with the exception of the fourth tentacle, which is but little larger than its repre- sentative in the antispadix. The cirrus of the first tentacle has become an enormous conical, fleshy organ. (Fig. 15.) The cirrus of the second has become flattened as well as enlarged, and bears num- erous rows of small glands upon one surface. (Fig. 16.) The cir- rus of the third is also flattened at its tip, and shows upon its ventral side many rows of fine pores. (Figs. 17 and 18.) The sheaths of the first, second, and third tentacles are completely fused and have de- veloped in accordance with the cirri, and now form a structure which Vayssiere has proposed to call the sheath of the spadix. (Figs. 13 and 14.) There is a grooye in the outer side of the sheath of the spadix, between the second and third cirri, into which the tip of the fourth cirrusis pressed. (Fig. 14.) The tip of this cirrus is overlapped by a broad flap, which corresponds to the smaller flap noticed upon the outer side of the antispadix. The base of the fourth tentacle lies within a notch in the sheath of the spadix and is not covered. Its own sheath is short and is free from the sheath of the spadix for a short distance only. In this respect the fourth tentacle of the spadix differs quite noticeably from the corresponding tentacle of the antispadix. Upon the outer side of the sheath of the spadix, and near its tip, is a large circular glandular area, slightly raised above the general surface. (Fig. 14, G.) The glandular area extends out TEXT-FIG 5,—Transverse sections of the spadix at successive levels. A, nearest the tip; D, nearest the base of the organ; 1, first cirrus; 2, second cirrus; 3, third cirrus; 4, fourth cirrus; S, slime gland of spadix sheath. 124 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. upon the flap covering the tip of the fourth tentacle. Upon its surface numerous pores, the openings of tubular glands, are easily seen. The bulk of the spadix is composed of the cirri of the first, second, and third tentacles. The fourth tentacle may almost be said not to enter into the formation of the spadix, so small is it compared with the mass formed by the other tentacles. (Fig. 19.) The cirri of the spadix are not of equal length, like those of the antispadix. Neither their bases nor their tips are at the same level. Text-figure 5 is intended to show the relative length and position of the cirri of the spadix by means of diagrammatic sections of four regions of the organ. In A, a section through the tip of the spadix, the fourth cirrus does not appear. In section B, taken a quarter of its length from the tip of the spadix, the tip of the fourth cirrus is cut through. In section C, taken just below the middle of the spadix, the second cirrus has ended, and in the position it occupied we see only bundles of muscle fibres passing from its base in the sheath of the spadix. The fourth cirrus is no longer completely shut in by the flap of the spadix sheath. In section D, taken through the base of the spadix, the third cirrus has disappeared in like manner as the second. In spite of the disappearance of two cirri the spadix has increased in size continually as we have approached its base. This is accounted for almost entirely by the great increase in the size of the first cirrus alone. But the fourth cirrus has also increased in size and is, at the base, included within the sheath of the spadix. Strands of muscle from the bases of the second and third cirri also form a portion of the organ. The fourth cirrus is still free from the sheath of the spadix back of where the tissues of the first cirrus and the sheath unite. Finally, the tissues of all the tentacles are united to form a solid base for the spadix, which is firmly attached to the posterior region of the cephalic sheath and the cartilage. Let us now turn to more detailed descriptions of the separate portions of the spadix. THE SHEATH OF THE SPADIX. This somewhat indefinite name is nevertheless convenient, and for this reason it seems appropriate and worth retaining. From the previous description and diagrams it will be noticed that in the anterior region of the sheath it is composed of the sheaths of the tentacles alone, but in its posterior or basal part it includes the muscle tissue extending from the bases of the second and third tentacles. Sometimes slight longitudinal grooves upon the outside of the sheath indicate the position and boundaries of the cirri within. (Fig. 13.) Upon the outer side of the spadix, i. e., the side turned away from the mouth, is a deeper groove which receives the fourth cirrus. The anterior end of this groove is hidden by the large flap developed on this side from the sheath of the spadix. This flap, extending along the entire length of the spadix, is widest near the tip of the organ, while it becomes a mere ridge near the base. The free edge of the flap is thin and evenly curved. It is about twelve millimetres in width at its broadest part. Examination of the sheath with a lens reveals minute pits upon the surfaces near its tip, numerous upon the outer surface and less so upon the inner surface. Except for these and the glandular area upon the outer side the sheath is quite smooth. The sheath is composed of an external layer of longitudinal muscle fibres, and of inner circular fibres ringing each cirrus cavity. It is covered by a single-layered epithelium, composed of slender columnar cells, the basal halves of which are occupied by elongate, oval nuclei. Goblet cells, filled with granular secretion, are found in exceedingly great numbers in the epithelium of the external surface of the anterior portion of the sheath, but in small numbers upon the basal portion. The pits and short grooves upon the anterior portion of the sheath, noticed under the lens, are lined mostly by mucus-secreting cells and serve the purpose of increasing the secretory surface. The epithelium upon the inner surface of the sheath is very similar to that upon the outer surface, except that the cells are shorter, the nuclei nearly round, and the goblet cells very rare. Indeed, the latter are only present near the edges of the cavities occupied by the cirri. Immediately under the epithelium is a dermis of felted fibrous and elastic connective tissue. In the thinnest portions this, containing a few muscle fibres, forms the entire substance of the MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 125 sheath. In the thicker portions the amount of muscle tissue within the dermis is very considerable, and is roughly arranged in the longitudinal and circular layers already mentioned. It must not be forgotten that a quite considerable portion of the sheath is derived from the tissues of the second and third tentacles after these have become continuous with the tissues of the former. The spaces between the mus- cles are occupied by fibrous and elastic connective tissue. The sheath is penetrated by a perfect network of vascu- lar lacune. Until we have some idea of the function of the glandular area upon the outer side of the spadix sheath the term ‘slime gland” will do very well to designate it. It is surprising that this structure should not have been mentioned by VayssterE in his excellent paper upon Nautilus. The slime gland forms a nearly circular area upon the outer side of the spadix sheath, from 25 to 30 millimeters in diameter, and is considerably raised above the surrounding surface, besides being of a much darker color, all in all being a quite conspicuous organ. (Fig. 14.) Numerous pores, the openings of the glands within, open upon its surface. The glands are formed of long, branching tubes, which are packed closely together, and occupy three-quarters of the thickness of the sheath at this point. (Fig. 57.) The sheath contains but little muscle tissue in this region, being composed almost entirely of fibrous connective tissue which, below the slime gland, is reduced to a network inclosing great numbers of vascular lacun of all sizes. The larger spaces have endothelial walls. The lacune are much more numerous than they are represented in Fig. 57, by far the greater number being too small to be shown in such a figure. The structure of the glands is quite simple. From a short, narrow neck arise several tubular outgrowths. (Fig. 57; Text-fig. 6, A.) Most of these are long and slender and extend into the sheath nearly at right angles to its surface. Around the outer part of the neck are often grouped short tubules or mere outpocketings of the wall. The main tubules may themselves be branched. The tubules of each gland lie parallel and close to each other, separated by only a small amount of submucous tissue. (Text-fig. 6, Aand B.) The tubules are packed together so that they form a package of almost equal transverse diameters from end to end. The tubules are lined by a single layer of . tall, col- umnar secretory cells. The lumens of the tubules are ex- tremely narrow, being rarely of greater width than half the height of the cells lining them. (Fig. 57.) The epithelial cells are extremely slender, averaging about 100 in length and 4/ to 8 in their transverse diameters. (Fig. 57, A.) The epithelium rests upon a thin basement TEXT-FIG. 6.—Slightly diagrammatic sections of a single gland of the slime gland of the spadix sheath. A, longitudinal section; B, transverse section. membrane. At the very base of each cell is a small oval nucleus, 34 by 8 in its dimensions. From just above the nucleus to its free end each cell is packed with deeply staining granules of 126 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. secretion. The region of the cell immediately about the nucleus is entirely free from any secre- tion, so that the outer edge of the tubule shows a clear border in sections. Figure 57 A shows a single cell of the secretory epithelium drawn with the aid of a camera lucida. It was taken from a place where the epithelium was lower than ordinary, but otherwise is characteristic. The single row of deeply staining granules almost completely fills the body of the cell. The bent base of the cell is a very characteristic feature, although not found universally. The short basal portion of the cell is direeted upward and inward, and the longer outer portion of the cell is perpendicular to the axis of the tubule. As the neck of the gland is approached a change takes place in the character of the epithelial cells. The epithelium becomes lower and the cells contain fewer and smaller granules. Finally the epithelium is only of about half the height of that in the tubules; the granule secreting cells disappear, and ordinary goblet mucous cells are found scattered in the epithelium, which is of the same character as that clothing the surface of the slime gland between the pores of the glands. At the edge of the slime gland are all stages between fully developed tubular glands and the merest invaginations of the surface epithelium. One might almost say that there is here an onto- genetic series in the development of the glands. The smallest invaginations are lined with epithe- lium entirely similar to that upon the surface of the slime gland. Farther from the edge the invaginations become deeper, and from the inner parts outgrowths occur which become the glandular tubules of fully developed glands. The young tubules possess an epithelium like that of the adult in its essential characters, but at first only a few cells appear to be glandular. These are typical goblet cells filled with finely granular secretion. In more developed glands the secreting cells become more numerous, the granules of secretion are larger, and finally all the cells below the neck of the gland are filled with coarse granules. The description of the glands upon the outer side of the antispadix was referred to this place. They are of the same character as those of the slime gland of the spadix, but are less developed. The glandular epithelium and the secretion are apparently alike in both organs. The glands upon the sheath of the antispadix are proportionately shallower and are less br: ranched than those of the spadix, but otherwise the structure seems to be the same. FIRST CIRRUS OF THE SPADIX. (FIG. 15.) The first cirrus is much the largest of the four forming the spadix. It is nearly circular in section, gradually diminishing in size from the base to near the tip. The latter diminishes in size very -apidly, ¢ , causing the cirrus to end in a point like the tip of a low cone. The tip is frequently excentric and is sometimes produced like a nipple. The surface of the cirrus is smooth except near the tip, where very faint annular grooves may be noticed. The base of the cirrus, its largest part, measures 32 millimeters dorso-ventrally and 17 millimeters from side to side. It is 6 centi- meters in length. From the ventral side of the base a strong muscle passes ventrally and across the body, to become lost in the tissues of the opposite side of the cephalic sheath. The main mass of the tissue of the cirrus passes immediately into the tissues of the posterior portion of the cephalic sheath on its own side. The development of a special muscle for this cirrus, as well as the remarkable muscular development of the cirrus itself, indicates that the cirrus is very actively employed at some time or other in the animal’s existence, and it may also indicate that the cirrus is extended or retracted as a whole from its base and is not extensile in the same manner as the cirri of other tentacles; but all statements of how this and the other cirri of the spadix are used are as yet guesses, pure and simple. Transverse and longitudinal sections explain the rest of the structure of this cirrus. (Figs. 52 and 53.) Near the center of the cirrus, but still to the inner side of it (i. e., the side nearest the buccal mass), is the large nerve N. This is surrounded by the transverse musculature of the cirrus. Around the core of transverse muscles is a thick ring of longitudinal muscles, which are divided by radial septa of transverse muscles. Outside this follow three thin layers of muscle— a circular, an outer longitudinal, and an outer circular layer. The essential features of the arrangement of the musculature are therefore the same as those of the digital or labial cirri. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. Hi A longitudinal section of the cirrus shows that the central transverse musculature consists of alternating layers of crossing fibres. (Fig. 52.) The section figured in Fig. 53 has been cut a trifle obliquely so that it passes through several of these alternating layers. The layers of muscles are arranged like the crossing boards of a double floor. The surface of the cirrus is covered by a fine columnar epithelium in which are scattered great numbers of goblet cells. The epithelial surface is increased by numerous pits the lining epithelium of which is especially supplied with secreting cells. The nerve of the cirrus is enlarged at regular and frequent intervals, like the nerves of the digital cirri. Each enlargement corresponds in position to a pair of the alternating layers of the transverse musculature. In a young Nautilus the first cirrus of the as-yet-undeveloped spadix is like one of the labial cirri, slender and marked with annular grooves. The corresponding seg- mentation of the cirrus and its nerve in the digital and labial tentacles has already been noticed. Probably there is a similar correspondence here, while the transverse musculature is also seg- mentally arranged. As the cirrus under discussion increases in size the external segmentation becomes obliterated. The branches of the nerve pass outward in the layers of the transverse muscle. The nerve ends abruptly near the tip of the cirrus. An artery runs along the inner side of the nerve A. The vein divides and its branches come to lie at a considerable distance from the nerve, V, V’, Fig. 53. Between the outer layer of muscles and the epithelium is a layer of connective tissue which is curiously developed in one region. (Fig. 52.) Over most of the cirrus the layer is thin and the tissue firm and close, containing a few muscle fibres; but just below the tip it is much thickened and great numbers of vascular lacune, large and small, make their appearance in it. The larger lacunee have endothelial walls. Fig. 52 only represents the larger lacunz, and not the far greater number of small ones. It may be possible that this forms a kind of erectile tissue. SECOND CIRRUS OF SPADIX. (FIG. 16.) The second cirrus of the spadix is much more modified than the first, for that is modified in shape and size mainly, while this has undergone modification of structure also. It is slender, and instead of becoming larger at its base it narrows. Its muscles are continued into the sheath of the spadix between the first and the third cirri. (Text-fig. 5,C, 2.) Its length is about 4 centimeters. Its basal portion, to within about 15 millimeters of the tip, is round and smooth. Exceedingly indistinct annular grooves can sometimes be seen in this portion of the cirrus. At the point referred to the cirrus begins to be flattened upon both dorsal and ventral surfaces. It ends ina flat, thin-edged, lancet-like tip. A little distance from the tip one edge remains thick while the other is thin, giving the cirrus a triangular shape. Concurrently with the flattening the cirrus becomes moré and more distinctly annulated, the grooves appearing a little more strongly marked upon the ventral than upon the dorsal surface. In general this cirrus adheres to the plan of structure already described for other cirri. The nerve, extending through the cirrus near its center, does not possess any unusual characters. It is of good size, showing ganglionic enlargements at regular intervals which correspond with the annulations upon the surface of the cirrus, and extends to the very tip of the cirrus. (Fig. 61, N.) Upon the inner side of the nerve is an artery, and still farther toward the inner edge of the cirrus alarge vein. (Fig.56,A and V.) The nerve and the artery are surrounded by transverse muscle fibres, but the radial arrangement of the musculature has been lost to a large extent and is replaced by an arrangement of the longitudinal muscles in lines extending across the cirrus in the direction of the shorter transverse axis, the dorso-ventral axis. In the round basal portion of the cirrus the arrangement of the muscles is similar to that in the digital cirri. The dorsal side of the cirrus, amounting to from one-half to one-third of its entire thickness, from the point where the annulations first show plainly, is occupied by glands and not by muscles. (Figs. 56 and 61, G.) The glands open by very minute pores in the annular grooves, a single row of closely placed pores occupying each groove. The pores of the glands are upon the slopes of the grooves and not in the bottoms. They are so small that they are only to be seen in sections. 128 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. The circular and outer longitudinal rings of muscles have been greatly reduced in this cirrus, the longitudinal having almost completely disappeared. Immediately underneath the glands is a thin layer of the circular muscles. With the development of the glands the dermis tissue has become greatly increased, so that now the glands are surrounded by fibrous tissue, traversed here and there by muscle fibres. Each gland has a thin tunic of muscle fibres. A few vascular lacunz are found in the dermis. The glands have the shape of thick, round-bodied flasks with very short and narrow necks. (Fig. 55.) Owing to their mutual pressure the glands are usually polygonal. They are 0.8 to 1 millimeter in length and 0.4 to 0.6 millimeter in diameter. The exterior of the cirrus is covered by an epithelium of very slender columnar cells, none of which are secretory. At the mouths of the glands a transition occurs to shorter or even cubical cells which line the duct and upper part of the body of the gland. The sides and the base of the gland are lined with exceedingly long, slender, secretory cells, whose oval nuclei lie in the very bases of the cells. There is considerable variation in the length of the cells of the upper side of the gland. Sometimes they are scarcely longer than those of the duct; sometimes, again, as long as any in the gland. Mucous cells are sometimes scattered among the cells of the upper sides and the duct of the gland, the other cells of these regions not appearing to be secretory; again, all are secretory. The portion of the secretory cell above the nucleus is closely packed with fine granules. The large lumens of the glands were in most cases filled with a finely granular secretion. Glands near the tip of the cirrus may be more or less distinctly divided into two portions, which are partially separated by ¢ constriction—a basal thick-walled secretory portion and an outer thin-walled portion, which may be a collecting or storing chamber, from which the duct leads to the exterior. The ridges upon the surface of the cirrus are almost entirely occupied by large vascular lacune. A network of connective tissue extends between the lacunz of the ventral ridges, but there is almost no connective tissue in the ridges of the dorsal side. THIRD CIRRUS OF SPADIX. (FIGS. 17 AND 18.) The third cirrus is the most highly modified and remarkable of the group. It is longer and larger than the second, being intermediate in size between this and the first. As has already been noted, its base lies posterior to that of the second. It is oval in cross section at the base instead of round, as is the case with all the other cirri of the spadix. It is narrowed at the base, however, like the second cirrus. For about half its length it is oval and perfectly smooth. At its middle it begins to be still more flattened dorso-ventrally, until near its tip it is almost per- fectly flat upon both sides. The dorsal side is apt to be somewhat concave and the ventral side convex. A longitudinal ridge may be present along the median line of the dorsal side near the tip, caused by the tissues passing over the nerve lying directly underneath. At the same time that the cirrus becomes flattened it loses its smooth surface. The dorsal surface becomes marked by transverse ridges, which are at first very faint, but become distinct as the tip of the cirrus is approached. At the very tip, however, the ridges become crowded and less distinct. They also disappear at the edges of the cirrus, leaving a smooth, unmarked margin. Close examination with the naked eye discovers many smaller ridges extending longi- tudinally between the transverse. It is upon the opposite (the ventral) side of the cirrus that we find a most peculiar structure. (Fig. 18.) Arranged across the cirrus in rows which seem to correspond closely to the ridges of the opposite side are great numbers of fine pits extending into the tissue of the cirrus. The largest of these may be a little more than a half a millimeter in diameter. Examination with a hand lens shows the openings to be nearly square, the sides being parallel to the main axis of the cirrus, and to be set as closely to each other in both directions as is possible. The openings are often so regularly spaced that they form longitudinal as well as transverse rows. Only a thin wall remains between the pits. At the posterior end of the pitted surface the pits become small, imperfectly formed, and finally disappear. Similarly the pits are not well developed at the tip of the cirrus. When the fingers are passed over the pitted surface it feels like shagreen, and MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 129 suggests that it is covered by a rough cuticle. This, however, is not the case, as we shall presently see. The middle part of the cirrus, where the transition from the oval to the flattened shape takes place, is triangular in section for a distance. (Fig. 59.) The inner side of the cirrus forms the short side of the triangle. The dorsal and ventral surfaces of this region bear their characteristic structures. The inner surface is smooth and muscular. In general the structure of this cirrus is so like that of the second that no detailed description is necessary of any part except the pits. In Fig. 59 we have a transverse, slightly oblique section of the third cirrus, and in Fig. 60 a longitudinal section of the same cirrus, both drawn with the aid of the camera lucida. Fig. 62 shows a longitudinal section through the center of a pit magnified to 34 diameters. The pits are simple cavities 1 millimeter in depth, into which a fleshy tongue projects from the posterior side as the animal is in its swimming position. Suppos- ing the cirrus to be placed tip upward, the tongue projects from the floor of the cavity. The cavity of the crypt forms only a narrow fissure about three sides and the edges of the fourth side of the tongue. This is thus attached to the wall of the crypt along a narrow median region. (Figs. 59 and 60.) The tongue is strongly muscular, the muscle fibres mostly extending from the base toward the tip. The tissue between the crypts is largely muscular; all the muscle fibres, both of the tongues and of the intermediate tissues, are much finer than those making up the body of the cirrus. Many connective tissue nuclei are scattered among the muscle fibres. Beneath the epithelium of the sides of the crypts and their tongues isa clear layer of a peculiar structure. (Fig. 62.) This layer does not extend quite to the bottoms of the crypts, but commenc- ing near here, becomes gradually thicker and thicker as the openings of the crypts are approached. The clear layer is especially thick upon the anterior edge of the crypt, i. e., wpon the edge toward the tip of the cirrus. Under low powers the layer appears homogeneous and structureless, but high powers of the microscope reveal numerous and exceedingly fine fibres in it. No nuclei whatever are found in the layer. At the extreme outer edge of the layer, immediately under the epithelium, no fibres at all, nor any other structural element can be distinguished. Passing inward, the fibres are progressively more and more distinct. Along the inner edge of the layer, next to the muscle, is a distinct layer of small nuclei which appear like connective tissue nuclei. It is this clear layer which gives the surface of this portion of the cirrus its hard character. It seems to form a supporting tissue or sort of exoskeleton for the other tissues of the crypts, or perhaps for the cirrus as a whole. The surface of the cirrus is covered with a single layered epithelium. Those portions of the cirrus not occupied by crypts are covered by an epithelium similar to that of the second cirrus. In the region of the crypts it is considerably modified. In the deepest parts of the crypts the cells are of about the same proportions as those upon the dorsal side of the cirrus— slender columnar cells, among which are numerous goblet cells. The number of secretory cells in these regions is not at all remarkable. As the cells extend outward upon the sides of the crypts and their tongues, they gradually decrease in length and increase in breadth, until a veritable pavement epithelium is formed. The outer portions of the sides of the crypts and all the area between their openings is covered by an epithelium of this character. The function of the crypts is entirely unknown, and I do not see that we have facts of any kind upon which to base even guesses as to the nature of their uses in the economy of Nautilus. The number of glandular cells in the crypts is so small that, as VAYSSTERE says, the latter can scarcely have been developed for the purpose of increasing glandular area. The development of muscle tissue about the crypts, and especially in their tongues, together with the development of a firm, hard layer upon their surfaces, indicates a considerable and important activity for these structures and for the cirrus as a whole as well. FOURTH CIRRUS OF SPADIX. (FIG. 19.) As has been said, this cirrus is almost unmodified. It is the smallest of the group and is nearly hidden by the flap upon the outer side of the spadix. It is scarcely longer than the 130 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. corresponding cirrus of the antispadix, but is of considerably greater diameter. The tip is flattened. Elsewhere the cirrus is nearly round. Its lower portion is smooth, while the distal half is more or less distinctly grooved. This cirrus has its origin at the very base of the spadix, and is free for almost its entire length from the main portion of this organ. It possesses a very short separate sheath which is not nearly as long as the sheath of the corresponding cirrus of the antispadix. (Figs. 12 and 14.) This sheath is united to the base of the spadix sheath. The base of the fourth cirrus passes under the base of the first cirrus to its outer side. Aside from the reduction of the annular ridges, the appearance of this cirrus is not markedly different from that of the digital cirri. The essential features in the structure of this cirrus are also almost the same as those described for the digital cirri. (Figs. 54and 58.) The arrangement of the muscles is somewhat modified by the great development of the transverse musculature, the strands of which are sometimes as large as those of the longitudinal muscles. The regular radial arrangement of the latter is largely lost. The epithelium of the annular ridges is not especially developed at any point, although distinctly higher upon the ridges than between them. Large blood spaces run within the ridges upon the inner side of the cirrus. They extend only a portion, one-half or less, of the distance across the inner face of the cirrus. These spaces are lined with flat endothelial cells, and communicate with veins lying deeper in the cirrus. They lie almost directly beneath the epithelium. They are not present in the small ridges near the tip of the cirrus, appearing in the tenth to the fifteenth from the tip, and increasing in size as the ridges increase in breadth and height. The nerves of the spadix come off from the left pedal ganglion; those of the antispadix from the right pedal ganglion. It is very difficult to trace the nerves into the individual tentacles, although I have succeeded in doing this in a few instances. The four nerves to the cirri of the spadix or the antispadix spring from the edge of the ganglion. They appear to belong to the superior labial series, but being a little larger. A few special nerves pass from the ganglion into the base of the spadix. One of these (Figs. 41, 30) forms an enlargement in the base of the spadix, from which several small nerves pass into the surrounding tissues. In a less than half-grown male the spadix formed a very small, flat organ, resembling the anti- spadix, which scarcely reached as far as the tips of the jaws. VayssreRE has already shown that the cirri of the spadix are at first like those of the antispadix, and that they undergo modification quite late in the life of the Nautilus. VAN DER HOEVEN’S ORGAN. Directly beneath the buccal mass of the male Nautilus is a peculiar organ discovered by Van pER Hogven and since known by the name used at the beginning of this paragraph. (Figs. 8,9, 10, 66, 67, 68, and 73.) To this organ an olfactory function has been ascribed, without any evidence, to be sure, but apparently in accordance with a common custom of describing any organ of Nautilus, the function of which is unknown, as an olfactory organ. The organ opens into a pocket formed laterally by the labial ridges, ventrally by the cephalic sheath, and dorsally by a ridge connecting the labial ridges. Into this pocket the anterior end of the organ projects freely. (Fig. 8.) The walls of the pocket soon attach themselves to the organ and, being continued upon its surface, forma tunic. This attachment takes place near the anterior end of the organ dor- sally, but near the middle ventrally. (Fig. 9.) The organ is oval, the long axis lying parallel to the long axis of the body, and is flattened dorso-ventrally. It is 25 millimeters in length, 15 millimeters in width, and 10 millimeters in thickness. If the pocket, or atrium, into which the organ projects be opened as far back as the attachment of its walls to the organ, we see that the anterior part of the latter is divided by a median longi- tudinal fissure which extends from the ventral side nearly through to the dorsal side of the organ. (Fig. 8, VF; Fig. 10.) The fissure does not extend on the surface quite as far back as the attachment of the integument to the organ. Transverse and longitudinal sections reveal the fact that the fissure just mentioned does, however, extend within the organ for some distance MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 131 into its posterior half, and that it communicates dorsally with a broad transverse fissure near the dorsal side of the organ. (Figs. 9 and 10, H.) The transverse horizontal fissure extends almost to the posterior end of the organ. The anterior free portion of the organ is firm in texture and is seen to be partly divided into lobes by fissures extending from the edges of the vertical fissure. In longitudinal and cross sections of the organ the deeper parts of the longitudinal fissure are seen to be bordered by thin, shelf-like laminz, which extend about halfway to the lateral edges of the organ. (Figs. 10 and 66.) The laminz do not reach the posterior part of the organ, extending only as far as the posterior end of the vertical fissure, which ends in a line directed upward and backward. The regions posterior to the lamin and dorsal and lateral to the horizontal fissure are glandular. The openings of the glands can be seen with the naked eye or a hand lens upon the walls of the horizontal fissure. The glandular part of the organ is quite distinctly different from the remainder in appearance and texture, but still is firm and hard. Both the lobules of the anterior region and the horizontal laminz radiate from a small region of firmer tissue near the anterior end and on each side of the vertical fissure. (Fig. 9.) The lobules noticed at the sides of the anterior portion of the vertical fissure are thick and fleshy and often have their edges rounded. Posteriorly they are seen to graduate into the horizontal lamine; as a matter of fact, lobules and lamin are differently developed members of a single series. Counting all as lamine, there are from 20 to 24 laminz upon each side of the vertical fissure. Several muscles are attached along the lateral edges of the anterior part of the organ. At their attachment they usually form a distinct muscular ridge from which two principal muscles separate themselves on each side. One pair of muscles extends backward along the sides of the organ to penetrate the muscular base of the buccal mass above and outside the ventral buccal retractors. (Fig. 8.) The other pair of muscles extends outward and each soon divides into two branches. The anterior branches are spread out upon the bases of the superior labial lobes. The posterior branches go to the sides of the cephalic sheath below the anterior. This arrange- ment of the muscles shows distinct resemblances to that of the muscles of the inferior labial lobe of the female. (Fig. 26.) A large nerve arises from the pedal ganglion just outside the infundibular nerve. (Fig. 41, 7 and 35.) The two nerves pass along the sides of the organ of Van pER Horven, entering it a little anterior to its middle. A branch from the tentacular artery of each side supplies VAN per Horven’s organ with blood. These are the same branches which, in the female, supply the inferior labial lobe. (Text- fig. 10, p. 182, 1 and 3.) The firm tissue forming so large a proportion of the anterior part of the organ is composed of a thick-meshed reticulum of elastic tissue fibres, in the interspaces of which run bundles of muscle fibres. The tunic is composed of a layer of muscle very distinct from the underlying tissues. The bodies of the lobules and the lamine are almost entirely composed of elastic tissue. The bodies of the thin horizontal lamin which lie hidden within the organ are not thicker, and frequently not as thick as the epithelium of either surface. The epithelium of the lobules and the lamine is of exactly the same character. It averages 80 in height, and is composed of a single cell layer comprising two entirely different sorts of cells. The more evident, and at first sight the only sort, are slender columnar cells from 5 to 8 in transverse diameter. Oval nuclei situated in the very bases of the cells make a distinct row along the lamin. All these cells appear to be able to form a secretion, which is contained in the cells in the shape of granules, which stain with remarkable intensity. But while all the cells appear to possess the power of secretion, not all in my preparations were exercising it. Next to areas in which all the cells were choked with secretion are areas the cells of which con- tained no secretion whatever. And as a rule, there is no gradual transition from one area to the other. The boundaries of the areas are distinct; upon one side all the cells are crowded with secretion, upon the other side not a singie cell contains any secretion. In only a few places are secreting cells mixed with others not secreting along the edges of the areas. Asa rule, the areas free from secretion are near the edges of the lamine turned toward the fissure (the Vol. 8—No. 5 3 137} MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. inner), while the outer parts of the laminz are covered by cells full of secretion. Occasionally, however, non-secreting areas may be found near the outer attached edges of the lamin as well. No secretion has been found in the cavity of the organ. The sum and substance of these facts probably amounts to this, that the secretory function of the epithelium of the laminz is exercised periodically only, and that my material was collected during the period of preparation, but before the entire secretory area had assumed its function. The epithelium of the laminz appears to be ciliated, and this appearance is connected with the presence of a second sort of cells in the epithelium. I have stained a number of preparations with borax carmine, and then with Lyons blue. Such preparations show a second line of nuclei at the level of the middle of the epithelium of the lamin. These nuclei are exceedingly slender, being 6 to 8 in length by 1m to 13 in width. They belong to and are situated near the center of long thread-like sensory cells, which stand thickly around the secretory cells. (Fig. 73.) The ends of the former project beyond the latter, forming sensory spikes, which are so numerous that they give the appearance of a thick coating of strong cilia belonging to the secretory cells. The cell bodies of the sensory cells are so slender and absolutely thread-like that they are not clearly visible without special stains, and then only in places where the other epithelial cells have been accidentally separated. Fig. 73 is an accurate drawing of such a place under a mag- nification of nearly 500 diameters, but taken from the glandular portion of the organ and not from the lamine. The sensory cells, however, are alike in both regions. Favorable cross sections of the epithelia show the nuclei of the sensory cells thickly clustered around and between the secretory cells. The bases of the sensory cells pass into the subepithelial tissue as fine fibres, and are there lost; but it seems only reasonable to suppose that they are directly con- tinuous with nerves, and that the cells are true sensory elements. We have now a better ground than before for supposing this organ to have a sensory function, which may very possibly be olfactory. ; The epithelium of the surface of the anterior parts of the organ and of the skin forming the walls of the atrium is of the same form as that of the lamin, though apparently not at all glandular. The glandular portion of the organ is composed almost entirely of long branched glandular tubules with narrow lumens. (Figs. 66,67,and 68.) The tubules are parallel to each other, while the submucous tissue separating them is so slight in amount as to form little more than a separating lamella. (Fig. 68.) The tubules are lined by a single-layered epithelium, composed, like that of the lamin, of secretory and sensory cells. The secretory cells are of a very different character from those of the lamine and probably produce a different secretion. The regular arrangement of their brilliantly staining nuclei in the bases of the cells causes stained sections to appear almost diagrammatic. I do not think that the histological condition of my material is good enough to warrant my making a detailed comparison between these cells and the secretory cells of the lamine. The regular arrangement of the tubules make the glandular region a striking feature of sections. The clearness of its secreting cells compared with those of the laminw, their slightly greater width, and the larger intensely staining nuclei are features which quite clearly distinguish the secreting cells of the glands from those of the lamin. The gland cells average 90 in length and are from 7s to 10 in width. The secretion collects in the shape of numerous droplets or granules in the portion of the cell above the nucleus. No secretion was found in the lumens of the glands. Around and between the secretory cells are sensory cells exactly similar to those described in the epithelium of the lamine (Fig. 73). The slender nuclei of the sensory cells form a quite distinct row at the middle of the epithelium. The sensory cells are not so numerous in the glands as upon the lamin, but still their number is surprising. Fig. 73 is drawn from a section in which the secretory cells had separated from the submucosa and each other, leaving the sen- sory cells revealed. The section was cut somewhat obliquely, and so does not show the free ends of the cells. The sensory cells are perhaps a little more numerous here than in most portions of MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 133 the glands, although the portion to be drawn was chosen at random. In a few places in my sections of the glandular portion of the organ I have seen the ends of the sensory cells project- ing beyond the surface of the epithelium as sensory spikes, but in most places the projecting parts were not present. Whether this is the normal condition or is due to poor preservation of the material I can not say. The nerves (Fig. 8, N) which enter each side of VAN peR HorveEn’s organ end in ganglia at the sides and near the posterior ends of the lamine (Fig. 41,35; Fig. 66, Gn). From the gan- glia a small nerve extends into each lamina (Fig. 66, N), and two or three nerves on each side pass into the posterior glandular region. Each nerve to the laminz is accompanied by a small artery. The laminar nerves possess an outer layer of ganglion cells as well as ganglion cells scattered throughout them. Each of the small lobular divisions of the anterior part of the organ receives a single nerve as well as the thin laminz. The facts described seem to me to constitute good and sufficient evidence for considering the inferior labial lobe of the female and VAN DER Horven’s organ to be homologous. The position in the body is the same; the principal muscles are very nearly alike; the innervation is the same; the course of their blood vessels is the same. It also seems probable that each lamina corresponds to one of the cirri or lamellz borne upon the inferior labial lobe of the female. The main evidence for this rests upon the innervation of the laminz, which is exactly similar to that of the cirri and lamelle of the inferior labial lobe. The structure of the nerves themselves is also the same in the two organs. The presence of a small blood vessel running close to each laminar nerve also constitutes a bit of evidence in favor of this view. The number of lamine in VAN pER Horven’s organ is the same as the number of cirri and lamellz combined of the inferior labial lobe, and the reasons for considering the cirri and lamelle of the latter to be homologous have already been brought forward. Finally the sensory cells add support to the view. It will be remembered that between the lamelle of the inferior labial lobe are pits lined by a peculiar epithelium. The cells of this epithelium appear to be exactly similar to the sensory cells scattered over the surfaces of VAN DER HokEvEn’s organ, and I think it not improbable, taking into consideration the other evidence for the homology of these organs, that during the course of the metamorphosis of the inferior labial lobe of the male, the sensory cells, which in the female are confined to limited areas occu- pied by them alone, have become distributed over the entire surface of the organ. The glandular part of VAN DER Horven’s organ, which forms so large a proportion of the whole, does not seem to correspond to any portion of the inferior labial lobe of the female. The gland is probably a new formation developed in accordance with the changed and special func- tions of the lobe. The inferior labial lobe of the female is evidently in much more nearly the primitive condi- tion, its parts being but little modified from the type of structure of the many simple tentacles around it. : Here, too, the question constantly arises, What are the functions of this organ‘ When any organ differs so much in the two sexes it seems only reasonable to consider that it is a sexual organ of some sort. We have, then, at least reasonable grounds for saying that Van pER HoEven’s organ, and possibly the inferior labial lobe, is an accessory sexual organ; but we know nothing whatever of its chief functions. Apparently its secretory functions are only periodically and not constantly active. To what use the secretion is put is impossible to guess, even if guesses happened to be desirable. The organ may be a sensory organ all the time and a secretory organ only part of the time, or both functions may be active only period- ically. In the latter case, again, the sensory function may be active only when the organ is not secreting, or this may be the time when the sensory function is most active, or the only time when it is active. It seems probable that the sensory function is either that of tasting or smell- ing. Possibly the activity of the secretory cells, or at least the flow of secretion, depends upon the perception of certain substances in the water by the sensory cells, or the sensory function may have a much closer relation to the everyday life of the animal. 154 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. OCULAR TENTACLES. There are four of these tentacles, two springing from near the base of the stalk of each eye. The eyes, it will be remembered, are attached to the sides of the head in the angle formed by the posterior edge of the lateral portion of the cephalic sheath and the projecting auricles of the hood. The ocular tentacles arise above the level of attachment of the eyes, one in front of, and the other behind, each eye (Fig. 1, O’ and O”; Fig. 2, O'; Fig. 38, O”). Accordingly, they are distinguished as the preocular and the postoc iat tentacles. The preocular is situated upon the base of the cephalic sheath, immediately back of the posterior corner of the sheath of the second digital tentacle, and in the angle formed by the projecting sides of the hood and the lateral walls of the head. Its sheath forms a portion of the posterior part of the cephalic sheath, only a few millimeters of its tip being free. The postocular arises above the posterior edge of the eye in the angle made by the hood and the sides of the head. It stands straight out from the sides of the head, having a free sheath 6 to 10 millimeters long. The preocular is directed outward and forward, the postocular outward and slightly backward. Both tentacles are well protected by the projecting sides of the hood. The cirri of the ocular tentacles are in their general features like those of the digital tentacles, but under the general similarity are most important differences of structure as well as of function. They are oval, lacking the angles of the digitals (Fig. 65). The annular grooves are very deep upon the anterior sides, and this is especially noticeable near the tips of the cirri (Figs. 64 and 63). OwerEn (1832, p. 14) well describes these cirri as ‘tin reality composed of a number of flat- tened circular disks appended to a lateral stem.” The closely pressed ridges project from the base to the tip of the cirrus like the lateral plates of a cephalopod gill. Observations made by Wriuey and published in the fortieth volume of the Quarterly Journal of Microscopical Science are well worth quoting in this connection: **The occurrence of aspecial tentacle in front of the eye and another behind the eye in Nautilus is well known. These tentacles resemble the large number of remaining tentacular appendages in being ringed and also in being retractile within sheaths, but differ from them in almost every other respect. In the first place, most of the tentacular appendages of Nautilus have essentially an adhesive function, to which is related a prehensile function. They are employed for seizing hold of food and for attachment to surfaces. . . ‘It will not be surprising to learn that the adhesive tentacles are not ciliated; but it is neces- sary to mention this negative fact, because the preocular and postocular tentacles are ciliated. On the side corresponding to the suctorial ridges of the adhesive tentacles the annulations of the preocular and postocular tentacles form deep grooves, between which the ridges project as promi- nent lamelle. The upper and lower surfaces of the lamelle and the bases of the grooves are covered with vibratile cilia. There can be but little doubt that the preocular and postocular tentacles of Nautilus represent tentacular processes, homologous with the adhesive tentacles, which have been modified to serve an accessory olfactory function. We will therefore speak of them as the olfactory tentacles, in contrast to the adhesive tentacles. . . . ‘The olfactory tentacles . . . . when extended stand out from ne body nearly at a right angle, the preocular tentacle being directed slightly forward and the postocular tentacle usually tending backward. The ciliated olfactory lamelle are directed strictly forward. ‘‘In the living Nautilus the olfactory tentacles otherwise offer a strong contrast to the adhesive tentacles by their almost uniform white color. When examined under the microscope there is found to be a little brown pigment in the annulations and at the edges of the lamelle, but when viewed in toto under water the general color effect is white. ‘** Moreover, the adhesive tentacles can be touched without necessarily being retracted, but at the slightest contact with a foreign body the olfactory tentacles are instantly retracted within their sheaths. The presence of accessory olfactory tentacles in Nautilus can, I think, be related to an essential bionomical difference between the existing Tetrabranchiata and the Dibranchiata. ‘Nautilus finds its food chietly by the sense of smell, while it is a matter of more or less MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 135 common observation that the Dibranchiata, with their remarkably perfect eyes, pursue their quarry by the sense of sight.” The structure of the preocular and postocular cirri seems to be the same in all respects. The annular grooves, which are so deep upon the anterior side, are frequently no more than grooves in the epithelium upon the opposite side; i. e., the groove is formed by certain of the epithelial cells being shorter than those of the remaining surface of the cirrus, the bases of all being at the same level. In other portions of the cirri the grooves affect the subepithelial tissues of the posterior side as well. The ridges upon the anterior face of the lower part of the cirrus are very thin and flat, are closely pressed together, and lie in a plane perpendicular to the axis of the cirrus. The ridges of the tip of the cirrus are not flat, nor of even thickness, are more separated from each other, and turn upward around the cirrus like portions of the rim of a saucer. They form little cups, open toward the tip of the cirrus. The epithelial cells of the cirri are all slender columnar cells. The cells of the bottoms of the grooves are taller than those upon the outer portions of the ridges. The former are about 60 in height and 4 in width. They are ciliated, the fine cilia being about 14 in length. The latter cells are only 44 in height. All possess oval nuclei irregularly located in the basal halves of the cells. Occasionally a goblet mucus cell is found among the ciliated cells. Goblet cells are frequent upon the posterior surfaces of the cirri and upon the unciliated portions of the ridges. The basement membrane upon which the epithelium rests is remarkable for its sharp outline and irregular surface. One can scarcely imagine a surface more wrinkled and pitted in a minute way. The outer surface of the epithelium, however, does not repeat this irregularity. The subepithelial tissue of the ridges is very scant, what little there is consisting of fibrous and elastic connective tissues, and containing few muscle fibres. From the structure of the cirrus, the side bearing the high ridges evidently corresponds to the inner side of the cirri of the other groups, although it is turned forward. Asa matter of fact, if the ocular cirri were pulled forward until they were parallel to the digital cirri, the now anterior sides would then be inner. For the sake of convenience in description and the comparison thus introduced, I shall speak of the anatomically anterior side, when needful, as the inner side. The arrangement of musculature is practically that which has been described as typical of the digital tentacles, except that it is even more regular in the ocular tentacles. As portions of the ridges are not constructed for adhesion there is no interruption of the arrangement of the muscles upon the inner side of the cirrus. Radially arranged longitudinal muscles surround the nerve, although this is, as in the former case, nearer the inner side of the cirrus than the outer. The two layers of circular muscle fibres and the outer longitudinal muscles pass uninterruptedly around the cirrus. The ocular cirri are especially well supplied with rather large blood vessels. It would be interesting to know if the arteries described by WILLEY as going to the eye do not also give off branches to the ocular tentacles, or if the latter are supplied from the tentacular artery. Upon the inner side of the nerve is an artery which corresponds in position to the artery of a digital cirrus. Several other arteries, perhaps branches of this, lie near the nerve. A large vein lies between the artery and the inner side of the cirrus. The structure of the nerves of the ocular tentacles is notable. (Fig. 64and65,N.) The nerves of the preocular and postocular tentacles arise as branches of a nerve which springs from the side of the pedal ganglion, the remainder of it being distributed to several of the digital tentacles. (Fig. 41,11.) A cross section of the ocular tentacles shows that their nerves are of unusual size. Near the tip of the cirrus the nerve has the same character as the nerves of the cirri already described. It has an outer layer of ganglion cells, thickened in each segment into ganglia. Shortly, farther from the tip of the cirrus, numerous bundles of nerve fibres join themselves to the inner side of the nerve trunk. As these pass toward the base of the tentacle they seem to gradually enter the nerve trunk, their places being taken by other nerve bundles from the outer parts of the cirrus. Thus a kind of accessory nerve is formed which extends from near the tip of the cirrus to its base along the inner side of the primary nerve trunk. (Fig. 65, N’.) These 136 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. nerve bundles are not surrounded by ganglion cells like the nerve trunk, so it is easy to distin- euish the boundaries of the latter in both longitudinal and cross sections. Nevertheless, they contain numerous nerve cells lying singly or in groups, some of the groups forming what one might call strands of nerve cells, parallel to the nerve bundles. At the base of the cirrus all the lateral bundles have entered the nerve trunk, which is here of the ordinary size. The nerve, as a whole, is enlarged in each segment of the cirrus by aggregations of nerve cells, the primary nerve trunk being the part most affected. From each ganglion twelve to sixteen nerves pass radially to different parts of the segment, especially to the lamella-like ridge of the inner side. These nerves are very large and distinct. The nerves passing to the ridges can be traced to directly beneath the basement membrane of the epithelium. I could not determine any direct connection of the nerves with cells of the epithelium, although, in view of the peculiar character of the tentacles and the epithelium of the grooves, and the very liberal and conspicuous inner- vation of these regions, it seems probable that future research will reveal special nervous elements in the epithelium. The most curious feature of the ocular tentacles is yet to be described. The tips of the cirri, consisting of several segments, or of a single terminal segment, break very readily. The ease with which the segments break off is explained by the presence in the cirrus of breaking planes, as I have called them. In longitudinal sections lines are seen stretching across the cirrus from erooye to groove, along which the connective tissues are weak or discontinuous. (Fig. 64, X.) The planes correspond to the grooves between each two segments. The longitudinal muscles and the nerve cord are not broken, but the muscles at least break very easily along the planes. Occa- sionally connective tissue nuclei are gathered along the breaking planes, though this may be a coincidence rather than a structural character. Atallevents, there seems to be here a provision for the amputation of segments of the preocular and postocular cirri with considerable ease. It would seem as if the retraction of the cirri within their sheaths at the slightest touch, as already quoted from WiLLEy’s published observations, would protect them from injury. And especially so, as they are situated in a nook under the auricle of the hood, back of the cephalic sheath, and above the eye, so that it seems as if they need be only partly retracted within their sheaths to be completely sheltered. I feel quite sure, from the constancy of these structures between all the segments of my sections, that they are not artifacts, although I do not by any means deny such a possibility. If they are natural struc- tures they appear to be a mechanism providing for the common and easy loss of (but not self- amputation, necessarily) terminal segments of the ocular tentacles, and they also point to the possibility of rapid regeneration of the lost portion, as is the case in other animals in which pro- vision is made for the easy loss of certain parts of their bodies. But it is also very strange that Nautilus should possess such a mechanism in the ocular tentacles when it also has the ability to retract them quickly upon a slight stimulus. The innervation of the ocular tentacles, as well as their position and structure, leaves no doubt but that they are members of the digital series which have become modified for sensory functions. To summarize: The digétal tentacles of both sexes are exactly alike in number, distribution, and structure. Their fused sheaths form the cephalic sheath, a fleshy wall surrounding the anterior portion of the head. Upon the inner side of the cephalic sheath of the female, above the funnel, is a lamellated region for receiving the spermatophore. The superior labial tentacles are alike in position and structure in both sexes, but are less in number in the male than in the female. The inferior labial lobes and tentacles are present in both sexes, but are quite different in each. In the female the lobe is large and muscular. Upon its anterior edge are numerous tentacles, some of which develop cirri, while others form lamellz, at the bases of which are certain sensory pits. In the male the lobe and its tentacles are represented by Van DER HOEVEN’s organ. The lamine of this correspond to the cirri plus the lamelle of the inferior labial lobe of the female, while the gland is not represented in the latter organ. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 137 The spadix and antispadix do not correspond to any group of tentacles in the female, as far as our present knowledge goes. It has been suggested that they have been formed by the separation of the four ventral tentacles of the superior labial group. It is true that the number of tentacles comprised by the spadix or the antispadix added to that of the superior labial group equals the number of tentacles in a superior labial group of the female, and that in young animals they are like these in size and structure. The innervation of the spadix and antispadix also seems to be like that of the superior labial tentacles. Yet the two organs are so completely separated from the labial tentacles, even standing entirely outside the labial ridge, that we must consider it still an open question if they are represented in the female until embryological evidence can be obtained. The ocular tentacles are members of the digital series which have become modified for sensory functions. This seems the best place to consider another secondary sexual character, which after all is closely connected with the tentacles. Both Vaysstrerr and Witiry point out that a difference exists in the shape of the opening of the male and female shells. In general the shell of the mele is larger than that of the female, and the breadth of the opening of the shell is greater in proportion to its height in the male than in the female shell. But these characters are so variable that in examining a large number of empty shells I was unable to determine which had belonged to males and which to females. Wr1iiry himself emphasizes the variability of this character. The hood of the male exceeds that of the female in size in the same manner as has just been mentioned for the opening of the shell. The generally larger hood and shell opening of the male seems to be largely the result of the growth of the spadix. PALLIAL COMPLEX. MANTLE. The mantle cavity of Nautilus extends completely around the body; it is shallow dorsally, but ventrally a deep, capacious cavity, which contains the various organs spoken of as the pallial complex. The mantle itself isa thin and only slightly muscular fold, which fits closely against the walls of the inhabited chamber of the shell. I wish to make a sharp distinction between the mantle and the body wall, especially between it and the thin, membranous portion of the body wall covering the visceral hump and so frequently spoken of as the mantle. I shall limit the term “mantle” in this description to the projecting fold around the middle of the body, extending for- ward from its junction with the body wall and elsewhere free from the body, surrounding it like a cape. The name can not properly be applied to any other portion of the body wall. The ventral and lateral edges of the mantle follow the edge of the shell and are attached to it it (Fig. 1, V M). From umbilicus to umbilicus, dorsally, the mantle forms a free fold, which lies against the involution of the shell (Figs. 1,2, and 5,D M). The most shallow parts of the mantle cavity are just beneath the umbilici of the shell, dorsal to each shell muscle. The edge of the mantle following the edge of the shell slopes rapidly upward and backward to the umbilici. The posterior limit of the mantle cavity also slopes upward and somewhat forward to the same point. Thus the depth of the mantle cavity or the width of the mantle, 10 centimeters in the mid-ventral line, is reduced to 1 centimeter over the shell muscles. The dorsal portion of the mantle is produced upward and forward and is closely pressed against the lower portion of the involution of the shell. In the mid-dorsal line, therefore, the mantle has a width, or the mantle cavity a depth, of about 4 centimeters. The dorsal part of the mantle cavity contains no organs, and is nearly closed off from the ventral part by the narrowness of the lateral portions, which are still more nearly closed by the upper ends of the crura of the funnel. The dorsal part of the mantle cavity must be nearly minimal in volume, since the hood and body wall forming its floor fit closely around the involution of the shell. The dorsal portion of the mantle is probably strongly contracted in alcoholic specimens, since it does not extend nearly as high up on the 138 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. involutions of the shell as the posterior face of the hood. It has been suggested that the black layer seen upon the lower portion of the involution of the shell is deposited by the dorsal portion of the mantle. The epithelium of the posterior surface of the hood is pigmented and glandular, and probably plays the principal part in the deposition of the black material. The mantle is for the most part a very thin, almost membranous, fold and is only slightly muscular. The contrast between it and the mantle of most of the Dibranchiata is very striking in this respect. The anterior border of the part of the mantle which is attached to the edge of the shell is slightly thickened and is comparatively quite muscular, forming a band along the edge of the mantle 1 centimeter to 1.5 centimeters in breadth. The median ventral portion of the mantle is also frequently especially muscular, and forms a strip which joins the muscular border like the stem of a T. The edge of the mantle is marked by two parallel grooves separated by a sharp ridge. The mantle seems to be attached to the edge of the shell, not only by its own edge, but also along a narrow band extending back from the edge on the outer side, along which the epithelium is peculiarly modified. Probably this attachment is not very strong. The dorsal portion of the mantle is of uniform thickness, and, while very thin, is still much more muscular than the yentral portion. The yentral portion of the mantle frequently presents a peculiar appearance. The tissues oneither side of the middle line seem to have become chitinized; the mantle in these spots appears thin, transparent, and structureless, and has the appearance of a thin sheet of chitin. Sometimes the chitinized areas (if we may so call them) are small, like oval windows set in the sides of the mantle; sometimes they extend oyer the greater part of the ventral portion of the mantle, and sometimes even across the mid-ventral line. In any case the thickened border of the mantle is notaffected. This change in the tissues of the mantle appears to begin on each side of the middle line ventrally and then to spread in all directions from the two starting points until nearly the whole of the ventral part of the mantle is affected. The question, Is this an accompaniment of senility ? can not help but be suggested. Speaking more exactly, the preceding description applies to the greater part of the ventral portion of the mantle, but not to all of it. There isa narrow posterior region which is thickened and which has hitherto been described as being part of the body wall. I wish to call especial attention to the fact that the posterior portion of the mantle of Nautilus is a true outfolding of the body wall, and that the renal sacs and the rectum are situated within this portion of the mantle and not inside the general body, as in the Dibranchiata. The pallial complex of Nautilus is entirely different from that of the Dibranchiata, not alone in its parts, but also in the relation of these parts to the body and to each other. This will be brought out as we proceed with the description of the separate parts of the complex. As the renal sacs lie in the posterior part of the mantle, this is consequently thickened and entirely different in its appearance from the anterior part. The renal sacs occupy only the cen- tral or most ventral region of the posterior portion of the mantle. They lie entirely between the posterior pair of gills. When the mantle is turned back and the animal turned ventral side up, as is usually done in examining these parts (Figs. 3 and 4), the renal organs sink more or less into the body, and the inner side of the mantle above them sinks down until flush with the surface of the body, so that the real relation of the parts is obscured. I presume that it is owing to this fact that the true position of the renal organs has been overlooked for so long by most observers. I can not understand from his words whether WirLeEy (1895) recognizes the same relations between the parts of the pallial complex as I do or not. However, if one cuts the mantle of a well-preserved specimen in the mid-ventral line while the animal is held in its natural position, there is no doubt whatever about the extent of the mantle nor of the positions of the renal sacs, rectum, anus, and gills, as well. The inner and outer walls of the posterior portion of the mantle fold are very thin and soft. Krrersrern described the thickened portion of the mantle as a projecting part of the body wall forming a posterior wall to the mantle cavity, upon which were located the anus, gills, and nephridial and pericardial pores. Owen describes the gills as situated upon the mantle. Jousry, however, certainly recognizes the real extent ot the mantle and the position of the various parts of the pallial complex. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 139 The discovery of the pallial arterial system is due to Wrmiry, who by means of injections was enabled to describe this peculiar system. The lesser aorta divides into two branches almost immediately after leaving the heart. One branch, the septal, goes backward and supplies blood to the siphuncle and the septal region of the body wall. The other branch, the pallial artery, bends downward to the middle line of the body wall and then runs straight forward below the skin on the surface of the renal sacs, and then in the median line of the ventral portion of the mantle nearly to its anterior edge. From its posterior part the pallial artery gives off branches to the intestine and the rectum. In front of the anus, at the posterior limit of the thin portion of the mantle, it gives off a large branch upon each side, the branchio-osphradial arteries. These supply the posterior portion of the mantle and ‘‘send up branches to the tips of the branchie, supplying the integument of the latter, and also a small branch into each of the osphradia. . . . In the female they also supply the nidamental gland.” As the pallial artery passes forward it gives off several small branches to the lateral portions of the mantle. Arriving near the edge of the mantle it divides into two branches, which turn to either side and follow the posterior edge of the muscular margin of the mantle, the marginal pallial arteries. Very numerous and regularly arranged short branches, the radial pallial arteries, spring from the ante- rior side of the marginal pallial arteries, while longer and more irregular branches pass from the marginal pallial arteries backward into the middle parts of the mantle. The marginal pallial arteries do not finally end in capillaries or blood sinuses, but unite with the pallio-nuchal branches of the dorsal aorta, thus forming a complete arterial circle, discovered by Winey, which he has named the circulus pallialis. The union takes place at the dorsal sides of the shell muscles. In addition to forming a union with the marginal pallial arteries, the pallio-nuchal arteries give off branches to the dorsal portion of the mantle, and to the dorsal nuchal region of the body wall (the region which is hollowed out to receive the involution of the shell), and to the crura of the funnel. In regard to the pallial veins Wriitry says the following: **When a Nautilus becomes moribund it usually rises to the surface, owing to an abundant production of gas in the interior of the body. If it is allowed to die and is then removed from the shell the veins are found to be injected with gas of some sort, and the finest ramifications of the veins, in the mantle at least, are displayed with a clearness which could hardly be attained by artificial injection. “The mantle is simply riddled by these veins in a manner which defies one’s powers of draftmanship. The veins are collected into two main trunks, which lie on either side of the anterior pallial artery, and proceed backward to open into the afferent branchial vessels. At the sides of the mantle there are also a number of lateral pallial veins, which open into a large sinus situated over the shell muscles.” The mantle of the specimen Owen described possessed a peculiar abnormality. Its opposite sides had grown together above the funnel so that Own describes and figures it as ‘* perforated by a large aperture through which the funnel passes.” BODY WALL. The inner side of the mantle cavity is formed by the body wall, to which I wish to devote a few words so as to lay a foundation for a point to be brought forward later. Laterally—i. e., at the sides of the body—the inner wall of the mantle cavity is formed by the sides of the great shell muscles alone (Figs. 3 and 4). These muscles pass from the cephalic cartilage outward and backward, forming the sides and part of the floor of the middle region of the body wall, to be attached one to each side of the shell just anterior to the edge of the last septum. Perhaps we might say that they end immediately back of the lateral portions of the mantle cavity, for these parts of the mantle cavity are limited posteriorly by the outer ends of the shell muscles. The muscles are only about 5 centimeters in length, but 2.5 centimeters in breadth by 1.75 centimeters in thickness. These dimensions convey an idea of what the power 140 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. of these muscles must be. The outer sides of the muscles are convex, the inner sides concave. The shape of the muscles in cross section is about the same as the shape of the area of attach- ment of the muscles to the shell. The muscles meet anteriorly, but as they pass outward and backward a considerable triangu- lar space is left between their ventral edges. This portion of the body wall is composed of quite a strong layer of transverse muscle fibres, which are continued, in part at least, outward over the shell muscles. The actual thickness of this region of the body wall is very little, but it is considerable when compared with that of the body wall covering the visceral region. The vena cava lies in the middle of the triangular space between the shell muscles. Between the dorsal edges of the shell muscles is another thin portion of the body wall, which forms the floor of the dorsal portion of the mantle cavity. This is also supplied with a quite strong musculature. This dorsal region of the body wall is concave, like a mold of the involution of the shell. It passes into the hood anteriorly and laterally, becoming gradually thicker and firmer. The shell muscles have a very copious supply of blood received through a number of arteries. The posterior columellar arteries are the largest and most important of those supplying the muscles. The left posterior columellar artery arises with the hepatic artery from a short common branch of the dorsal aorta—the hepatico-columellar artery. (Text-fig. 10, p. 182.) The columellar artery takes a diagonal course upward, outward, and forward to the upper edge of the left shell muscle, immediately anterior to its attachment to the shell. Then, bending downward and back- ward upon the inner surface of the muscle, it gives off numerous branches which penetrate the muscle. The right posterior columellar muscle arises from the right side of the dorsal aorta about 7 millimeters anterior to the origin of the hepatico-columellar muscle. As the posterior portion of the dorsal aorta lies upon the left side of the body, the right posterior columellar artery has a longer course to run to reach the right shell muscle than the left posterior columellar artery has to reach the left shell muscle. Otherwise the course of the two arteries is the same upon their respective sides. From the point where each posterior columellar artery bends downward a branch is given off to the region of the mantle in front of the shell muscles and to the portion of the body wall dorsal to it. The anterior portions of the shell muscles are supplied with blood by a branch of each innominate artery. These (the anterior columellar arteries) pass backward, downward, and outward to the muscles. (Text-fig. 10, p. 182.) In addition to these special arteries to the shell muscles, the nuchal arteries, or their branches pass along the inner dorsal edges of the muscles and appear to send small branches into them. The shell muscles are innervated from the visceral ganglia. Exceedingly numerous flattened band-like nerves pass from the posterior side of each ganglion into the muscles. (Figs. 41, 14.) GILLS. The two pairs of gills are situated upon the mantle at the sides of the ventral mantle chamber. (Figs. 8 and 4). They are arranged as an anterior anda posterior pair, one gill of each pair lying upon each side of the mantle, close to each other. The gills of Nautilus differ from those of the Dibranchiata, not only in number, but also in that they are situated upon the mantle instead of upon the body wall, and in that they are attached by their bases only, otherwise lying freely in the mantle chamber. They haye.much the same shape and structure as the gills of the Dibranchiata. The gills are situated upon the thin and muscular part of the mantle just below the convex anterior angle of the outer end of the shell muscle, the base of the anterior gill lying about 8 millimeters in front of the base of the posterior gill. The bases of the gills are sometimes placed so closely to each other that they seem, as OWEN said, ‘teach pair arising by a common peduncle from the inner surface of the mantle,” though I have never found this to be literally true. Examination always has shown that the bases of the gills were separate from each other. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 141 Though there is rarely any considerable difference in the size of the gills, it will usually be found that the gills of the anterior pair are thicker than those of the posterior pair, while the latter may be a trifle the longest. Average measurements for the anterior gills are 18 millimeters in width and 11 millimeters in thickness. The posterior gills are 15 millimeters in width and 9 millimeters in thickness. Both pairs of gills are about 5 centimeters in length. Each gill is composed of two rows of flat, crescentic leaflets attached alternately to the sides of an oval stem. Although the posterior gills possess somewhat the smallest bulks, they bear more leaflets than the anterior gills, having about sixty-five pairs, while the latter have only about fifty-five. Owing to the arrangement and shape of the leaflets the gills are flattened dorso-ventrally. The number of leaflets varies considerably in different specimens, being as low as thirty in some. The leaflets are attached upon the stem obliquely to the base of the gill. The leaflets of the tip of the gill are rudimentary; they become more complex toward the base of the gill, being com- pletely formed at about the tenth from the tip. It will be noticed that in this description I have apparently reversed the position of the gills as given by previous observers. This is explained by the fact that others have described the gills in the position they occupy after the mantle has been reverted, and as though they were attached to the body wall. Owen recognized the pallial position of the gills, but later observers, with the exception of Joupry, seem to have assumed that the gills are upon the body wall, and this makes the posterior and anterior gills of their descriptions correspond to the anterior and posterior gills of my description. The stems of the gills are flattened at their bases in the plane of the greatest width of the gills to form thin plates. (Fig. 4, at the end of the index line B V.) The lines of attachment of the stems of the gills to the inner side of the mantle are directed upward, forward, and slightly outward. The anterior gills lie a little to the outside of the posterior gills. The branchial vein runs along the ventral side of each gill as a projecting ridge. The branchial veins of the anterior gills run inward from the bases of the gills toward the median line, suspended by a thin liga- mentous band, which may be considered as an inward extension of the base of the stem of the gills. (Fig. 4,BV.) At the outer borders of the inner renal sacs the veins pass inward through the mantle toward the heart. The lower leaflets of the anterior gills extend inward for some “istance upon the ligamentous support of the branchial veins. Each leaflet is composed of two parts, a central or basal supporting portion of the same tissues as the stem of the gill and an outer folded respiratory portion. (Fig. 23.) A branch of the branchial vein passes along the outer edge of each leaflet. Between the smooth basal part of the leaflet and the collecting vein the leaflet appears to be ridged. In reality it is not ridged, but folded or tucked, and the folds of the tucks alternating upon one side with those of the other side form the apparent ridges. The sides of the folds, however, have fine folds nearly at right angles to the edges of the primary folds. Along both edges of the folds are small blood vessels running at right angles to the marginal vessels of the leaflet. The branchial vein lies upon the surface of the gill, forming a projecting ridge. Above the branchial vein the leaflets of the opposite sides of the gill are united to each other in such a way as to form a longitudinal septum extending between the vein and the stem of the gill. There is no branchial canal in the gill of Nautilus. Upon the dorsal side the leaflets project considerably beyond the stem of the gill, which is thus hidden in a groove between them. The stem is con- siderably wider upon its dorsal than upon its ventral edge, and thus the leaflets come to be quite widely separated dorsally. As the tip of the gill is approached the stem narrows. Toward the base of the gill the dorsal side of the stem is produced into a sharp ridge. From the distal end of the ridge to the tip of the gill the stem is marked by transverse grooves, extending from side to side between successive pairs of leaflets. The branchial arteries pass outward from the vena cava through the posterior walls of the nephridial chambers. Here they form outpocketings into the glandular appendages upon both sides of the walls. From here the arteries pass into the mantle and run in it along the bases of the gills until they reach the middle of the attachment of the gills to the body. At this point they turn and run along the ventral side of the stem of the gill to its tip. I have never been 142 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. able to find the valves mentioned by OWEN as existing in the branchial arteries at the bases of the gills. The minute structure of the gills of Nautilus pompilius and macromphalus has been studied by Joupry. He considers that the thickened stem of the gill of Nautilus forms a structure which is comparable with the glands he has described in the gills of other Cephalopods, which are organs in which the blood corpuscles are formed. The stem is covered externally by a layer of muscle fibres which also pass outward along the concave edge of each leaflet. The stem is composed almost entirely of connective tissue, in which the glandular elements are disposed at several points. Near the outer surface of the stem is a layer of quite large vascular lacuns, incompletely lined with flattened endothelial cells. The lacune are separated only by thin lamelle of con- nective tissue. The lacune also extend outward into the supporting portion of each leaflet. Only very small lacunz are found in the center of the stem. In the middle of the outer side of the stem a large vein is constantly present, extending from the tip of the stem to near its base, where it opens into the branchial artery. In the central portion of the stem, but still near the median vein, are a number of lacunze which, instead of being empty, like those at the surface of the stem, are filled with large granu- lar cells, each possessing a large nucleus. These may be foyind throughout the remainder of the gland (or stem), scattered here and there in the connective tissue. JouBIN considers that the central region is the only portion presenting an aspect comparable to that observed throughout the whole of the glands of othe Cephalopods. The remainder of the stem (gland, Journ terms it) is formed of connective tissue, in which large numbers of muscle fibres are scattered. The concave border of each leaflet is thickened, the thickening being due to a lateral extension of the tissues of the stem of the gillinto each leaflet. (Fig. 23.) It forms the supporting part of the leaflet, as well as containing portions of the branchial gland. It contains very numerous vascular lacunze, which differ in their arrangement from those of the stem in that the larger lacune are in the central portion, while the smaller lacunz are external. The lacunz receive blood from the afferent vessel of the leaflet. .Here and there are free cells in the lacune similar to those observed in the principal part of the gland. All this region of the leaflet is covered with tall, columnar, epithelial cells. The outer ends of the cells bear a distinct border. The thin respiratory membrane is covered with large, flattened, epithelial cells. A great number of lacunz penetrate the inner part of the membrane, scarcely separated by a network of connective tissue cells. A band of muscle continued from the surface of the stem passes outward along the side of the afferent vessel turned toward the respiratory membrane. In places the muscle projects into the afferent vessel and is bathed by the blood flowing in it. The blood reaches the gill through the branchial artery which runs along the inner side of the stem from the base to the tip of the gill. (Fig. 23, 2.) Two sets of vessels are given off from the branchial artery. Upon opening the artery two rows of large alternating openings are seen in the wall turned toward the leaflets. These lead into the afferent vessels of the leaflets, which run along the concave side of each, close to the edge of the respiratory membrane. Two other rows of alternating openings, smaller than and median to the first, lead into vessels which pass into the stem of the gill. From the afferent vessels of the leaflets smaller vessels arise which pass at right angles to the first along the entire length of the upper edges of the primary folds of the respiratory mem- brane. Opposite each secondary fold is an opening in the wall of the vessel of the primary fold through which the venous blood passes into the lacune of the secondary fold, where the inter- change of gases between the blood and the water takes place. In a similar but inverse manner the arterial blood is collected from the secondary folds into efferent vessels lying along the lower edge of each primary fold. These unite in a vein following the outer or convex border of each leaflet, which vessels themselves unite with the branchial vein. From the afferent vessels of each leaflet the blood escapes through several openings into the MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ; 143 lacun of the supporting portion of the leaflet. These are in communication with the lacunee of the stem of the gill, and so the blood passes from the leaflets into the stem. From the lacun of the stem it is gathered into the median longitudinal vessel lying near the surface of the stem. During its passage through the stem and its lateral extensions the blood has caught up many of the free cells of the branchial glands, which now form new blood corpuscles. They are carried by the longitudinal vessel into the branchial artery at the base of the gill, and thus into the circu- lation. It will be noticed that all the blood passing through the stem of the gill is venous, and that, having made this short circuit, it passes again into the branchial vein, the greater part then passing through the branchial leaflets into the systemic circulation. An observation made by WrLLey on a young Nautilus is significant. Describing it, WILLEY Says: : “The youngest individual I have as yet obtained was a male with the following dimensions: Millimeters. Length from root of siphuncle to mid-anterior point of hood (measured along the dorsum) ------------------ 25 Length of hood in middle line. ......-..---.------------- +--+ ----- += 22222 eone ence n nner renter neces 10.5 Breadth of body across middle of eyes. ..-.---.-------------------- +--+ 2-2 terre renee rere Sepace 15 “The surface of the hood was perfectly white and unpigmented. The branchiz of opposite sides were in close apposition in the median line, and, curiously enough, the larger posterior pair extended forward far into the interior of the funnel. ‘The shell was perforated at the umbilicus, as it is throughout life in J. umbilicatus.” If this specimen was a typical one of the young Nautilus it is evident that the gills are moved outward toward the sides of the body as the animal approaches maturity, a fact which possesses still more interest when we remember that the rudiments of the gills of the Dibranchiata arise close to ihe median line of the body, on either side of the anus, and that they move to the sides of the body late in development only. The branchial nerves are two large, flattened, band-like nerves, one of which arises from the posterior side and near the inner end of each visceral ganglion. (Fig. 41,22.) They run directly backward, along the ventral body wall, to the posterior limit of the mantle cavity. Here they turn outward and forward in the inner wall of the mantle fold. After giving off a couple of small branches which apparently supply the walls of the renal sacs, the nerves fork near the bases of the gills, and a branch passes into each gill. (Fig. 41, 19 and 20.) The later shifting of the gills to the sides of the body may account for the peculiarly exposed course of the branchial veins of the anterior gills. (Fig. 4, BV.) INTERBRANCHIAL AND PREANAL PAPILLZE. Just in front of the base of each posterior gill is a small papilla upon the inner surface of the mantle. (Fig. 3, IP.) The papille are about 2 millimeters in height and width. It is to these papilli, situated between the bases of the anterior and posterior gills, that I apply the name interbranchial papille. In the median line of the ventral part, just in front of the line limiting the thin portion of the mantle, two papilla project from the inner surface of the mantle. (Figs. 3 and 4, PA.) Each papilla has the shape of a bilobed transverse ridge, and usually the two are fused, forming a distinct ridge across the median line of the mantle. It is only rarely that the papille are separate, and even then the separation is so slight as to be scarcely noticeable. Wiuiey describes a case in which the interval between the papillee was 2.5 millimeters. The sometimes total separation and nearly constant partial separation of the two parts of the ridge leads me to describe it as two papille fused rather than as a single papilla. The united papille have usually passed, heretofore, by the name of postanal or supra-anal papille. As it is readily demonstrated that they are situated upon the inner surface of the mantle and not upon the body wall, they can not be postanal except when the mantle is turned back and the natural position of the parts of the pallial complex is reversed. To avoid this difficulty I suggest that they be called the preanal papillee. In 1883 Lankesrer and Bourne first called particular attention to the interbranchial l44 . MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. papille, calling them osphradia, and suggesting that they correspond to the osphradia found so widely distributed among the Mollusca. Their specimens were not sufticiently well preserved to allow an histological examination of the papille, so the hypothesis depended entirely upon the evidence of their innervation. LaNKESTER and Bourne describe a small nerve as arising from the nerve to the anterior gill near the fork of the branchial nerve and running into the papilla. This innervation corresponds to the innervation of the osphradia of other Mollusca. Witiey (1895) describes a small nerve proceeding to the osphradium of LANKESTER and Bourne from the point of bifurcation of the branchial nerve. He also suggests that the preanal papille represent a pair of osphradia, *‘corresponding metamerically with the pair described by LankesteR and Bourne between the bases of the gill plumes.” This suggestion is based upon the form, and variations in form, and upon the innervation of the papille. It has already been stated that the halves of the preanal ridge may be entirely separated, and that they are always distinctly marked. Wittey finds that a small nerve arises beside (inside of) each visceral nerve and runs back- ward close to it. Arriving at the point at which the visceral nerves bend outward, the inner nerves continue near the median line, passing into the mantle; they were traced through the nidamental gland of the female. In regard to the relation of this nerve to the preanal papilla Wiuey says: ** The inner and smaller visceral nerve passes over the region of the renal sacs on each side to the base of what I may call the posterior osphradia, to which it undoubtedly sends nerve fibres, although I can not say positively that I have definitely traced these.” In another place in the same article he says: ‘‘As to the innervation, I will say at once that it is very difficult to see the actual nerves or nerve fibres (because the nerves are often not compact trunks, but broken up into loose strands) which pass into the osphradia; but the anatom- ical relations of the visceral nerves to the osphradia, which, I think, have never been fully described, are such as to leave no doubt as to the source from which the osphradia derive their innervation.” Wittey called attention to the fact that these two papille have essentially the same topo- graphical relations to the anterior gills which the osphradia of LANKEsTER and Bourne have to the posterior gills. **Their greater proximity to the middle line is shared in common with the posterior (anterior) renal sacs and apertures and even the posterior (anterior) branchial veins, as compared with the corresponding anterior (posterior) structures. That they are bifid, and therefore more highly developed than the anterior (posterior) osphradia, is in keeping with their position in the living Nautilus in the anterior region of the mantle cavity, and also with the fact that the posterior (anterior) branchie, with which they would be associated in the metameric system, are considerably larger than the anterior (posterior) branchie.” The words in parentheses indicate the relative natural position of the organs, Wimury having described them as they appear after the mantle has been turned back. WILLEY’s argument for the metameric relation of the anterior gills and the preanal papille appears to be strengthened by the fact that in the young specimen already mentioned he found the gills closely approximated in the middle line, and in that case the preanal papille could not have been far from the bases of the anterior gills. In a later article WiLLEy gives more interesting facts in regard to the structure of the osphradia. ‘* By means of macroscopic sections of fresh material the presence of vibratile cilia on the sensory epithelium of both the inner and outer osphradia can be demonstrated, and this I regard as the final proof of the osphradial character of the so-called postanal papille. The sensory epithelium of both osphradia is distinguished from the surrounding ectoderm both by the presence of the cilia and by the general absence of goblet cells. The olfactory lamella of the accessory olfactory tentacles (the pre- and post oculars) and the sensory epithelium of the osphradia are the only places where I have observed vibrating cilia in Nautilus hitherto.” A set of serial sections of the preanal papille of a male brought to light an interesting structure inthis. Inthe base of each papilla is a gland composed of a number of irregular branching tubules. (Fig. 69,G.) Each opens separately to the exterior through a very minute pore. The MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 145 tubules increase in size toward the ultimate branches. They are lined by a single layer of not very tall columnar cells, the nuclei of which stained deeply while the body of the cells remained unstained and clear. That the cells are secretory is proved by the fact that the cavities of the glands were filled by a secretion, the granules of which were so fine that it appeared homogeneous under ordinary high powers. These glands may be the homologues of the glands Kerr described as being scattered over the area between the preanal papill and the nidamental gland in the female. I find the same area continuously glandular and much thickened. (See p. 147.) The epithelium had been entirely rubbed off from the surface of the interbranchial papillz and the preanal papille, of which I made series of sections. Therefore, I have no personal knowledge of its character. As regards the innervation of the papill, serial sections do not reveal any such abundance of nerves as we should expect, were they sensory organs of importance. The edge of the ventral part of the mantle possesses a remarkavle number of nerves, many of considerable size. This being the fact, we have a right to expect that the innervation of sense organs of the importance of osphradia will have an at least equally plentiful supply of nerves. Instead of this being the case, serial sections do not show any nerves whatever passing into the interbranchial or preanal papillae. The large nerve of the posterior gill is seen running by the base of the interbranchial papilla, but neither in dissections nor in serial sections have I seen any nerve pass from this into the papilla. I do not wish to be understood to deny that the interbranchial and preanal papille are osphradia, but I do wish to call attention to the fact that they are not yet proven to be osphradia. Wuury admits, and calls attention to the fact, that he has not been able to absolutely trace any nerves into these papille. He goes very much farther than the known facts warrant when he regards the presence of vibratile cilia **as the final proof of the osphradial character of the postanal papille.” While it is true that sensory organs are frequently covered by a ciliated epithelium, among the cells of which the special sensory elements are nestled, the fact that certain portions of the body of an animal are ciliated does not in and of itself constitute proof that these portions of the body are sensory organs. The final proof as to whether or not these papille of Nautilus are osphradia must be, besides the presence of special sensory cells, their innervation; and at present both these points are very much in doubt. The nature of the nerves of Nautilus, to which WILLEY has called attention, and the position of these papille with respect to the course of the nerves, render an investigation of their innervation quite difficult. The morphological importance of osphradia is too great to permit of any assumption of their presence in Nautilus without complete proof. It is because I do not consider that the osphradial nature of the papilla under discussion has been proved beyond any doubt that I have used the name **interbranchial papille ” for the papillee which have been called the osphradia of Nautilus ever since the publication of the paper by LanKesrer and Bourne. This is suggested as a provisional name until such time as the true nature of these papille shall have been proven. RENAL AND PERICARDIAL PORES. The renal organs are situated in the posterior portion of the mantle fold, their presence causing the considerable thickness of this portion of the mantle. The glands situated upon the anterior branchial arteries are shoved together in the median line below or anterior to the rectum. The glands situated upon the posterior branchial arteries are just outside and behind those already mentioned. So that we can with justice speak of anterior and posterior renal organs (Fig. 36). The anterior renal sacs lie beside each other on either side of the middle line; the posterior renal sacs are separated by the two anterior renal sacs. Each renal sac communicates with the exterior by a slit-like opening situated upon the inner side of the mantle. The openings of the posterior renal sacs are at the inner ends of the bases of the posterior gills (Fig. 3, R P). The openings of the anterior renal sacs are located at the inner ends of the bases of the anterior gills, or near where the anterior branchial veins pass through the mantle into the body (Fig. 3, R A). Upon the inner side of each anterior renal pore is another opening, the pericardial pore (Hios3 bak): 146 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. Each renal or pericardial pore is surrounded by a lip, a raised thickened portion of the mantle. The pericardial pores are the largest of the six, being 3 millimeters in length. The renal pores are each 2 millimeters in length. The lips of the latter are divided into inner and outer parts, forming tight valves. The main axes of the pores are all directed obliquely backward and outward. ANUS. In the median line of the mantle, just posterior to and above the anterior renal sacs, is the anus (Fig. 3, A). Its edges are plaited and project slightly from the surface of the mantle. The anus is situated upon the thickened posterior portion of the mantle, about 8 millimeters from the line along which the mantle joins the body wall. The anus of VALENCIENNES’s specimen was situated upon the body wall between and at the middle of the shell muscles. VALENCIENNES has shown himself too good an observer for us to consider that he made a mistake in this description and figure. It was simply a very peculiar and rare abnormality. REPRODUCTIVE APERTURES. The reproductive apertures of both male and female Nautili are paired. The two differ from each other in the same sex, and the right apertures are differently formed in the two sexes. The apertures of the female present the simplest conditions. The aperture of the functional oviduct is upon the right side of the body, at the tip of a projection from the body wall (Fig. 4,O V), immediately anterior to the crease formed by the junction of the mantle with the body wall and about halfway between the right shell muscle and the median line of the body. The transverse slit-like aperture is borne upon a dorso-ventrally flattened plaited projection of the body wall. This projection, which forms the tip of the oviduct, is, in preserved specimens, of a dark-brown color. The color is the same as that of the nidamental gland, which Witey tells us is a bright yellow in the fresh condition; so the tip of the oviduct may also be of a very different color in the living than in the preserved specimens. It forms a projection 12 millimeters in width, 5 millimeters in thickness (dorso-ventral measurement), and 10 millimeters in length. The length of the dorsal side is not quite so great as that of the ventral side. The walls are thick and transversely folded, and are evidently glandular. In spite of its comparatively large size the tip of the oviduct is not a conspicuous part of the pallial complex, being situated so low in the crease formed by the mantle and the ventral body wall. The aperture of the left reproductive duct is an exceedingly minute pore on the left side of the body, in the crease formed by the union of mantle and body wall, and located imme- diately posterior to or above the base of the posterior (the smaller) gill. The position and form of this aperture are the same in both male and female Nautili. The aperture leads into the organ commonly called the pyriform sac, which there seems to be good reason to consider as the vestige of the left reproductive duct of Nautilus. It has the same structure in both sexes. The functional male efferent duct opens at the tip of the penis, a tubular organ lying in the median line of the ventral body wall. (Fig. 3, P.) The tip of the penis only is free from the body wall. The cavity of the penis is divided a little back of the tip of the organ by a longitudinal partition into two portions, which are parallel for a certain distance. They then fork, the left branch turning outward and backward toward the minute left reproductive aperture, and soon ending blindly. The right branch continues to the right to that region of the crease between the mantle and the body wall where the tip of the oviduct is located in the female. It here penetrates the body wall and becomes continuous with the vas deferens. Just back of the penis, which term refers to that median structure within which the efferent ducts are parallel to each other and finally unite, and are contained within a common wall, the right duct is swollen to form a considerable sac, the spermatophore sac. This forms a protrusion of the body wall which is quite noticeable. The structure of these parts will be described in more detail in the section treating of the reproductive organs. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 147 NIDAMENTAL GLAND. Immediately in front of the preanal papille of the female a large pleated gland is situated upon the inner side of the mantle. (Fig. 4, N.) This has been called the nidamental gland. In the fresh condition it is of a light yellow color, but when preserved its color is a dark brown. The nidamental gland extends across the mantle nearly the entire distance between the bases of the anterior gills. It has been called kidney-shaped. It is shaped as a number of thin, closely pressed, parallel folds would be if their ends were bent around close to their middle portions until the opposite ends nearly meet each other. Most of the folds of the gland are thus continu- ous around the curved ends of the organ. The infolding has taken place toward the anterior side of the main portion of the gland. The gland is about 60 millimeters in width, and 25 millimeters to 32 millimeters in length. At its edges the mantle is raised, forming a border entirely around the gland. On the posterior side and between the anterior and posterior portions of the gland the border thus formed is only a low ridge. Upon the ends and the anterior side of the gland the raised mantle forms a fold which overlaps more than half of the inturned portions of the gland. The outer surface of the ridge of the mantle is smooth, and the inner surface as well of the overlapping anterior parts. The inner surface of the other parts of the border is ridged per- pendicularly and is apparently covered by an extension of the glandular tissue of the gland. By means of the raised border of the gland a canal is formed which enters the anterior side of the gland and branching, extends to each side between the anterior and posterior portions of the gland. Owen suggests that the divisions of the nidamental gland serve ‘‘ both to conduct the secretion nearer the orifice of the oviduct, and also to prevent its being drawn within the respi- ratory currents of water, and so washed away as soon as formed.” If the channel between the different portions of the gland serves to conduct the secretions of the gland, it is difficult to see how it conducts them near the orifice of the oviduct with its open end directed away from the oviduct and its lateral branches ending under the overlapping border of the gland. The parallel glandular folds of which the organ is composed are quite separate in the anterior portions, but are grown together closely in the posterior portion. Medianly, between the ends of the anterior portions of the gland, is a thickened, apparently glandular, projecting portion of the mantle. In the center of this is a low, longitudinal ridge. (Fig. 4, Y.) The gland is supplied with blood through branches of the branchial arteries. A large blood lacuna lies in the median. line in the mantle below the nidamental gland. This breaks up into numerous smaller lacune in the thickened portion of the mantle between the ends of the gland. In a half-grown female the nidamental gland was just forming. The mantle was scarcely thickened, but the outlines of the different portions of the gland were already marked out by the border formed by the raised fold of the mantle. The glandular area was covered by very fine parallel ridges, scarcely visible to the naked eye. The gland was of the same color as the sur- rounding portions of the mantle. Kerr has described a series of glands between the preanal papillae and the posterior side of the nidamental gland. The apertures, ‘‘to the number of about 150, form a band about 0.5 millimeter in width, curving gently forward on either side of the postanal papilla, tapering off and terminating close to the advehent vessel of the posterior gill. In section these openings are seen to be the apertures of tubular ducts which pass inwards perpendicular to the surface for some little distance and then break up into several blindly ending branches. These are lined by involution of the surface epithelium, which, in the neighborhood of each aperture, increases to about twice its thickness elsewhere, its cilia at the same time becoming long and powerful (0.03 millimeter in length). Once within the narrow aperture the lumen of the tube expands to about 0.05 millimeter in diameter, and the lining epithelium becomes shorter, the remainder of the lumen being lined by comparatively short columnar cells, each with a round ellipsoidal nucleus.” In some females this area is greatly swollen, forming a single elongate gland. It is not possible, then, to distinguish the separate apertures of the glands upon the surface. I have not yet been able to determine if the glands in the bases of the preanal papille of the male are homologous Vol. 8—No. 5——4 148 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. with the just mentioned glands upon the mantle of the female. Their structure is certainly very much like that of the glands described by Kerr. As the epithelium of the inner surface of the mantle had been rubbed off in my specimens, I can not say anything about its structure. It is strange that Wri.ey should have overlooked the ciliated surfaces described by Kerr. Kerr’s observation certainly weakens WILLEY’s ‘final proof” regarding the osphradial nature of certain papillx, for this is proof that other regions of the body, aside from the surfaces of the grooves of the ocular tentacles and the interbranchial papille and the preanal papille, are ciliated. The glandular area is differently developed in different females of various ages, and this I take to be an indication that it forms an accessory part of the female reproductive apparatus. Let us now sum up the observations on the pallial complex. The mantle is continuous around the body, forming a broad ventral fold fastened along its edge to the edge of the shell, and a small free dorsal fold, connected by very narrow lateral portions. In conformity with this struc- ture there is a capacious ventral mantle cavity containing all the organs collectively forming the pallial complex, and a small dorsal mantle cavity; the two are connected by shallow lateral cavities. The pallial complex consists of the following parts: The anus; two pairs of gills; two pairs of nephridial pores; one pair of pericardial pores; two interbranchial and two preanal papille, which may be osphradia, corresponding metamerically to the gills; one pair of reproductive apertures; in the female, the nidamental gland. ; All these parts of the pallial complex, except the reproductive apertures, are situated upon the inner side of the mantle. The latter are situated upon the body wall. The renal sacs-also might be considered as forming parts of the pallial complex, for they are situated within the base of the mantle. This arrangement of the parts of the pallial complex of Nautilus is very interesting when compared with the Dibranchiata, in which all the organs mentioned are located upon the body wall. The arrangement of the organs of the pallial complex of Nautilus is the same as in many Gastropoda. FUNNEL. The funnel is an organ of great size, not to be overlooked in the most casual glance at the animal. While showing a general similarity to the funnel of the Dibranchiata, it also presents differences of the utmost interest to the student of comparative anatomy. Lying closely pressed against the ventral side of the head and nuchal regions, it has a length of about 8 centimeters and a breadth of 4 centimeters. (Figs. 3, 4, and 6.) The width of the funnel varies greatly in pre- served specimens, depending largely upon the state of contraction of the organ. It forms an extremely solid mass of tissue. Its posterior end extends well into the mantle cavity. The anterior end lies partly in the ventral groove of the cephalic sheath, and its tip extends a very little beyond the posterior border of the ventral notch of the cephalic sheath. (Figs. 7, 24, and 25.) The funnel forms a long cylinder, but instead of being closed, like the funnel of the Dibranchiata, it is open upon the ventral side, where its edges merely overlap each other. It is as if the edges of a flat, oblong piece of tissue had been inrolled about the longitudinal axis until their edges slightly overlapped. wee ihe iG Clue whe = Sonn 10 @ MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 1 Text-Fic. 11.—THE LESSER AORTA AND ITS BRANCHES, VIEWED FROM THE DORSAL SIDE. radial pallial artery. 11, siphuncular artery. marginal pallial artery. 12, left septal artery. arteries of nidamental gland. 13, common septal artery. rectal arteries. 14, artery of pyriform sac. , intestinal artery. 15, posterior viscero-pericardial aperture. , heart. | 16, dorsal aorta. , gonaducal artery. | 17, lesser aorta. , genital artery. | 18, pallial artery. , right septal artery. 19, branchio-osphradial artery. , accessory siphuncular artery. 20, median pallial arteries. od | 188 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. either side of the anterior pallial artery, and proceed backward to open into the different bran- chial vessels. At the sides of the mantle there are also a number of lateral pallial veins, which open into a large sinus situated over the shell muscle.” The peculiar perforated structure of the vena cava, together with the large size of the hemocel, may have an important bearing upon the ability of the Nautilus to endure being suddenly hauled to the surface without suffering apparent ill results. The specimens which I have bad the privilege of studying were captured at a depth of from twelve hundred to eighteen hundred feet. At the latter depth they would be undera pressure of eighty atmospheres. Pro- fessor Worcester has told me that while the Nautili came to the surface uninjured, other animals brought up with them, as fish and crustacea, were always dead upon reaching the surface. It is evident that something in its structure must account for the ability of the Nautilus to withstand such sudden and tremendous changes of pressure, though this function may be, and probably is, only a concomitant of the structure and not its principal function. In order that a change of pressure should not prove injurious to an animal it is only necessary that the internal pressure of the tissues should remain equal to the external pressure. It seems to me that this result would be easily accomplished in Nautilus in the following manner. The pressure of the surrounding water upon the body would be transferred immediately to the blood contained in the hemoceel. The cavity of the hemoccel is in direct communication with that of the vena cava, and consequently with all the vascular spaces of the body, through the holes in the dorsal wall of the vena cava. By this means the pressure of the blood in the hemoceel is directly transmitted to the blood of the entire body, and thus the pressure within and without the body is equalized. No change in the yolume of the body would occur because the volume of the hemoccel and ecelom is minimal, and because of the incompressibility of the fluid. The hemoccel is completely closed from the exterior, so no water enters it, or anywhere comes in direct communication with the blood. It seems entirely improbable that water ever enters the coelom through the pericardial pores, as has been suggested. NERVOUS SYSTEM. (FIG. 41.) The central nervous system of Nautilus consists of three ganglionic bands which unite so as to form a ring around the esophagus, two passing ventrally to the cesophagus and one dorsally. The dorsal band represents the cerebral ganglia plus their commissure (12). The ends of the band are sometimes slightly larger than the central portion, but there is never any such separa- tion of the parts as to allow us to say, these are the cerebral ganglia, or this is the cerebral commissure. The posterior of the ventral bands represents the pleuro-visceral ganglia (13); this also is not separated into a pair of ganglia and a commissure, although the ends of the band are sometimes larger than the central portion. The anterior ventral band is composed of two distinct ganglia united by a slender commissure, the pedal ganglia (28) and the pedal commissure (29). The pedal ganglia are flat and crescentic in outline. The cerebral, pedal, and pleuro-visceral ganglia form a junction at the sides of the cesophagus. The pleuro-visceral ganglia seem almost to join the pedal ganglia rather than the cerebral, but closer examination proves that they unite with the cerebral ganglia to as great an extent at least as with the pedal ganglia. I shall speak of the cerebral and pleuro-visceral ganglia as if each band were in reality < single ganglion. From each outer side of the cerebral ganglion an enormous optic nerve passes outward into the stalk of the eye (24 and 25). The base of the optic nerve is swollen and may form an optic ganglion, a point which the study of sections alone will settle. The optic nerve is almost immediately divided into numerous parallel small nerves which in passing outward twist slightly about the axis of the nerve. They are much more closely pressed in the stalk of the eye than nearer the cerebral ganglion. At the back of the retina the nerves separate and form a mesh about this bowl-shaped organ. Near each end two nerves pass from the anterior side of the cerebral ganglion forward to 5 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 189 the ventral side of the buccal mass, where they enter the buccal nervous system (5 and 6). These are the outer and inner cerebro-buceal connectives of each side. The buccal connectives are of considerable length. In preserved and contracted specimens they are found to make numerous loops, which provide the extra length required when the buccal mass is thrust forward. The buccal nervous system consists of two pairs of ganglia united by connectives and two commissures passing anterior to the cesophagus. The cerebro-buccal connectives pass through the muscular membrane which covers the ventral surface of the buccal mass and unite with the pharyngeal ganglia—slender ganglia lying at the sides of the ventral surface of the buccal mass, immediately upon the lower edge of the mandibular muscles (4). The pharyngeal ganglia are united by the long pharyngeal commissure passing anteriorly along the edge of the lower jaw (2). From the posterior ends of the pharyngeal ganglia strong connectives extend backward and inward to the buccal ganglia at the sides of the esophagus as it issues from the buccal mass (82). The buccal ganglia are quite small. They are connected by a commissure passing around the anterior side of the esophagus (33). Numerous nerves are given off by the pharyngeal ganglia to the mandibular muscles. A nerve arising on the posterior side of the buccal ganglion bends over the dorsal side of the latter and passes to the salivary gland (34). A small nerve passes from the buccal ganglion to the cesophagus (31). Other nerves seem to pass into the tongue, but could not be accurately traced. A number of small nerves (more than a dozen) leave the anterior side of the cerebral ganglion between the bases of the inner cerebro-buccal connectives and pass forward upon the dorsal sur- face of the buccal mass (27). Some of these nerves or their branches enter the mandibular muscles. The majority of them pass into the space between the folds of the buccal membrane and are distributed to the papillee along the edge of the membrane. A few small nerves (23) leave the posterior sides of the outer ends of the cerebral ganglion and pass to the posterior portion of the dorsal buccal retractors close to their attachment to the cartilage. These seem to be the same nerves which VALENCIENNES describes as proceeding to the cavity of the cartilage which he mistook for the otocyst. In one specimen I have been able to trace the otocystic nerves. They are small, of about the same size as the nerve figured as going to the post-ocular tentacle. Each arises from the dorsal surface of the cerebral ganglion, just above the base of the optic nerve. As the otocyst is pressed between the posterior surface of the pedal ganglion and the cartilage, the otocystic nerve passes into the angle between the cerebral and pedal ganglia and then runs along the posterior surface of the pedal ganglion. The tunic of the nerve is so closely attached to that of the pedal ganglion that the nerve seems at first sight to spring from this ganglion. The nerve spreads out fan-wise upon the surface of the otocyst. The nerve of the rhinophore seems to leave the cerebral ganglion close to the base of the optic nerve, but I am not entirely sure of its course. No nerves are given off from the inner edges of the pedal ganglia, but from the outer edges arise exceedingly numerous closely set nerves. These nerves are distributed entirely to the funnel, the labial tentacles, and the digital tentacles and the cephalic sheath. In other words, they pass only to those parts which some consider to be homologous with the foot of other mollusea. The infundibular nerves are a pair of large nerves leaving the inner end of each ganglion, passing forward and downward into the tissues of the funnel (8). They are situated at either end of the pedal commissure, from which no nerves arise. For the first part of their course the infundibular nerves lie in a cavity slightly larger than themselves, probably a blood space. Just outside the infundibular nerves two conspicuous but smaller nerves (7) pass forward from the pedal ganglia to the inferior labial lobes in the female or to their homologue in the male, VAN DER HorveEn’s organ. The nerves enter the base of the inferior labial lobe; they enter VAN DER HorveEn’s organ at about the middle of each side. In each case after the nerves have entered they expand into small ganglia (35), from which nerves are given off to the separate tentacles of the organs. Fig. 41 is drawn from a male specimen in which the nerves pass inward from the ganglion instead of forward as in the female. 190 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. The outer edge of each pedal ganglion is fringed with numerous fine nerves. These nerves may be separated into two groups. The first of these are small, very slender nerves, which spring from the anterior or upper side of the edge of the ganglion. These nerves go to the tentacles of the superior labial groups: in the male, the nerves of the spadix and antispadix also are included in this series. The nerves of the tentacles of the spadix are, however, much larger than the nerves of the superior labial tentacles, or of the tentacles of the antispadix. In one dissection I found a quite peculiar nerve (30); it passes from the left pedal ganglion into the base of the first cirrus of the spadix, where it ends in an enlargement from which a number of small branches proceed into the surrounding tissues. The apparently similar innervation of the superior labial tentacles and the tentacles of the spadix and the antispadix points to the latter being separated portions of the superior labial groups. But it is not safe to rely overmuch upon the, at present very slight, evidence of the innervation. The nerves arising from the pedal ganglia are too little separated for us to distinguish accurately between one group and another. The second series of nerves are much larger than the first and arise from the lower or pos- terior portion of the edge of the ganglion, or even from the side pressed against the cartilage. They proceed to the individual digital tentacles (9). Several large nerves leave the upper (or outer) ends of the pedal ganglia, near the junction with the cerebral and pleuro-visceral ganglia. From these nerves (10) branches proceed to some of the digital tentacles and to the hood. Finally, a large nerve leaves the pedal ganglion very close to its junction with the other ganglia. The two main branches into which this divides become the nerves of the preocular and postocular tentacles. Finer branches proceed to the posterior portion of the hood, and some- times to cirri of digital tentacles. Numerous nerves, large and small, arise from the posterior edge of the pleuro-yisceral ganglion. The nerves of the two sides are separated by a narrow median interval free from nerves. On either side of the interval a large visceral nerve (22) leaves the ganglion and runs straight backward, lying upon the inner surface of the body wall at the side of and parallel to the vena cava. At the posterior limit of the mantle cavity the visceral nerve turns outward and forward in the mantle, finally dividing into two branches which extend into the gills (19 and 20). Before the visceral nerve divides to form the branchial nerves I have found it to give off two branches, which seemed to pass into the posterior walls of the renal sacs (17 and 18). Just before the visceral nerve bends into the mantle it gives off small nerves to the spermatophore sac and genital duct (16). Frequently connected with the visceral nerves are a pair of slender nerves which pass to the dorsal wall of the vena cava (15 and 21). These are, however, very variable in their origin. Always present, they sometimes both arise from the visceral nerves at about the middle of their course in the body. Sometimes both arise directly from the pleuro-visceral ganglion just inside the origins of the visceral nerves, as is figured by WiLLry; or one may arise from the pleuro- visceral ganglion, while the other springs from some portion of the visceral nerve, as is shown in Fig. 41. Witey is quite sure that these nerves innervate the preanal papille, and partly for this reason considers the papille as the anterior pair of osphradia. I have not been able to trace the nerves anywhere but to the walls of the vena cava; although this does not constitute proof that they end there. LanKASTER and Bourne state absolutely, WriLEy with confidence, that they have traced a small nerve from the bifurcation of the branchial nerves into the interbranchial papille. This branch also I have been unable to find, either in several dissections or in a series of sections of the papilla. Outside the visceral nerves a number of nerves of various sizes leave the pleuro-visceral ganglion and extend into the shell muscles and the body wall (14). The number of these is much larger than is represented in Fig. 41, only the larger ones being drawn. From the extreme ends of the pleuro-visceral ganglion a few very small nerves extend into MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 191 the posterior portion of the hood. From its innervation, which is derived from the cerebral, pedal, and pleuro-visceral ganglia, the posterior portion of the hood seems to be fairly compar- able with the dorsal portion of the nuchal region of the Gastropoda. EYE. The eye of the Nautilus is bowl-shaped, to use a rough comparison, the top of the bowl being * closed by a thin membrane which is perforated centrally by a small round hole, while the base of the bowl projects as a short stalk which is attached to the side of the head (Fig. 1, E). The top of the bowl is turned outward. The eye does not seem to be round, but somewhat triangular, the rounded apex being directed ventrally. It is 22 millimeters in length (antero-posteriorly), 15 millimeters high (dorso-ventrally), and 12 millimeters from the base to the outer side. The stalk of the eye is 9 millimeters in diameter, but only 2 or 3 millimeters long. The edge of the eye.is produced into a flange ventrally and laterally, but not dorsally. The round aperture in the outer face of the eye is usually spoken of as the pupil and leads into the cavity of the eye lined by the retina, there being no lens or any medium of refraction in the eye. The sea water has free ingress to or egress from the cavity of the eye. The pupil is about 2 millimeters in diameter. From the ventral side of the pupil a groove leads across the face of the eye to its ventral edge. The posterior edge of the groove projects over the groove to the opposite side, transforming this into a tubular channel. Usually the edges and the center of the face of the eye are slightly raised, leaving a depression between them. Except for a few almost microscopic depressions of the surface, the face and sides of the eye are quite smooth. The outer epithelium of the eye is composed of long, slender ciliated cells. The groove on the face of the eye is lined with a similar epithelium. Von HENSEN suggests that a constant stream of water may be driven through it, keeping the pupil clean, and preventing the entrance of foreign bodies into the eye. The membrane forming the outer face of the eye is quite thin; | millimeter thick at the edges, it gradually becomes thinner until the pupil is reached, where it is scarcely thicker than writing paper. The sides of the eye are much thicker than the outer face, and they increase in thickness as they approach the stalk. The dorsal side is about 1.5 millimeters in thickness; the ventral side is double this thickness. The capsule of the eye is composed for the most part of connective tissues; a little muscular tissue is also present. In longitudinal section the cavity of the eye is oval with a blunt outer and somewhat pointed inner pole. The wall of the outer portion of the cavity is of an intense black color. This black area is approximately circular. The side and back walls are of a light gray color, the line of demarkation between the black and gray portions of the wall being very sharp. The difference in color is caused by the fact that in the posterior portion of the cavity the retina bears rods which hide the pigment, while the rods are absent on the anterior portion of the retina. I follow Hatuer’s account of the structure of the retina. The retina is about 1 millimeter in thickness at the posterior side of the cavity, gradually becoming thinner as it passes anteriorly. The branches of the optic nerve spread out in a thin fibre layer immediately beneath the retinal epithelium. The epithelial layer of the retina is composed of two kinds of cells. The first are columnar cells, having a width equal to about one-eighth of their height. The nucleus lies in the upper end of the lower third of the cell. Fine pigment granules lie in the cell above the nucleus, but rarely below it. The second kind of retinal cells are much more slender than the first, almost thread-like in shape. The nucleus usually lies at the beginning of the upper third of the cell. The pigment granules are larger than in the broader cells, and often are so large compared with the width of the cell body as to be arranged like a string of beads. They also frequently extend below the nucleus. The broad and fine cells alternate regularly. The pigment does not extend quite to the upper end of the cell, nor often into the lower third of the.cell. Thus the pigment forms a dark band which is very noticeable in sections of the eye. 192 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. The rod layer which covers the gray portion of the retina is composed of slender rods of equal size. The rods are about three times as long as the retinal cells. Each rod is composed of an axial cord which stains deeply in carmine, and of a lightly staining cortex. The epithelium of the retina is separated from the nerye-fibre layer by a thick basement membrane, through which the nerve fibres penetrate and enter the retinal cells. The nerve fibres enter the broad retinal cells just above the nucleus. The bases of the fine retinal cells are continuous with nerve fibres. RHINOPHORE. (Figs. 21 and 22.) Between the stalk of the eye and the projecting posterior edge of the cephalic sheath is an organ, probably olfactory, which has lately been compared with the rhinophore of certain Gastropoda, and to which this name is applied. It is a small pyramidal protuberance of the side of the head, located on a horizontal line with the lower edge of the stalk of the eye. The body of the eye projects over the rhinophore, completely hiding it when the Nautilus is not viewed from below. The posterior side of the rhinophore is produced into a finger-like process of about the same height as the pyramidal base; the whole is 8 or 10 millimeters in height. The process is not annulated and is ‘not retractile” (WiLLEY, 1897, 1), and bears no resemblance nor relation to the digital tentacles. It may be well to speak of this as the tentacle of the rhino- phore. Just dorsal to the tentacle is a pit 6 millimeters in depth and 2 millimeters in diameter (the dorsal pit). On the anterior side of the base of the tentacle is the opening of another pit, narrower but much deeper than the dorsal pit. This is the fossa of the rhinophore. It is 10 or 12 millimeters in depth, extending into the tissues of the head in a line directed inward and downward, except as the last 2 or 3 millimeters of the tube turns sharply forward. The base of the fossa is near the otocyst, and Kerrersrer thinks that this is what Macponatp mistook for the otocystic canal. From just within the external opening the fossa is continued upward in the center of the tentacle nearly to its tip. The walls of the fossa are much folded longitudinally and are lined by a single-layered ciliated epithelium of slender columnar cells. Among these are many cells which remind one strongly of the olfactory cells in some of the vertebrata. The middle portion of these cells is swollen, forming a large, spherical, clear body which is distinguishable in sections viewed under low powers. The proximal and distal ends of the cells seem to be exceedingly slender and thread-like. These cells are limited to the walls of the fossa. The epithelium of the dorsal pit is like that of the outer surface of the rhinophore. A large nerve appears to leave the anterior side of the cerebral ganglion just under the point of union of the cerebral and optic ganglia, and, lying close to the fossa, extend to the tip of the tentacle of the rhinophore. The body of the rhinophore is composed for the most part of dense elastic connective tissue, though in the base of the organ are some muscles. KEFFERSTEIN describes the tentacle of the rhinophore as ‘tein zungenformiger Lappen - . . der wie eine Klappe die Miindung seines Axenkanals schliessen kann.” In preserved specimens the tentacle frequently is folded down over the mouth of the fossa, but this is apparently due to its being pressed upon the eye, so that the tentacle is probably in an unnatural position. OTOCYSTS. The otocysts of Nautilus pompilius lie upon the front side of the cartilage immediately back of the pedal ganglia, and near the junction of the latter with the cerebral and pleurovis- ceral ganglia. They are ovate in form, measuring about 3.5 millimeters in the direction of their long diameter. The end of the auditory nerve spreads out over the surface of the otocyst. The otocyst is a thin walled sac almost completely filled by an immense number of elliptical crystals packed closely together. The crystals vary in thickness between 0.0011 and 0.0066 mil- limeter, and in length from 0.0033 to 0,014 millimeter. The crystals are composed of calcium carbonate, giving characteristic chemical and light reactions. They all have the shape which would be assumed by a perfect crystal of dog-tooth spar if all its angles were rounded. Very MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 195 frequently cases of the twinning of two or more crystals are seen. In instances where two crys- tals are twinned the angle between their axis is usually 78°, any divergence from this angle being quite small, so far as observed. When twinned the ends of each crystal are as perfect as in single crystals. The union of two or several crystals forms the cross and star-shaped bodies, “ete.” mentioned by MacponaLp. CARTILAGE. (Fig. 40.) In the region of the bases of the digital tentacles is a large and strong cartilage which affords a firm place of attachment for the major muscles of the body. It is composed of a central por- tion which Owen has termed the body, from each side of which a pair of processes project dorsally (the cephalic processes) and ventrally (the infundibular processes). The cartilage slants from above downward and forward, the ends of the cephalic processes reaching dorsally to the body wall of the nuchal region immediately back of the hood and in front of the crura of the funnel, while the infundibular processes extend into the funnel through the inner wall of which they show as white lines. The greatest width of the cartilage is 3 centimeters, the length between the tips of the proc- esses is 4.75 centimeters. The infundibular processes have a length of 2.5 centimeters, the cephalic processes a length of 1 centimeter. The cephalic processes are round and end squarely. The muscles of the digital tentacles, the labial tentacles, and the spadix are attached to their anterior faces. The shell muscles find an attachment upon their posterior faces. The infundibular processes are much broader than the cephalic as well as thinner and nearly flat. Their broad anterior faces are turned somewhat inward as well as upward. These faces are slightly concave, while the outer and posterior faces are slightly convex. The tissues of the anterior portion of the funnel are attached to the lower portion of the anterior faces, while the muscles of the posterior portion and of the crura of the funnel are attached to the posterior faces of the infundibular processes. The pedal ganglia lie against the upper portions of the anterior faces of the infundibular processes, while the pleurovisceral ganglia are supported by the median processes of the body of the cartilage. The body of the cartilage is bent downward and backward in the middle, forming a sharp reentrant angle anteriorly and a projecting point posteriorly. From the upper portions of the anterior side of the body of the cartilage a pair of small processes project toward the median line, the median processes (m. p.). The muscles of the buccal mass, the inferior labial lobe or Van per Horven’s organ, and the levator muscles of the funnel, are attached to the body of the cartilage. The points of attachment of the latter muscles are marked by the dotted lines at L i. in Fig. 40. The body of the cartilage is penetrated by two veins on each side. These enter widely sep- arated upon the anterior side, but leave the cartilage close together upon the posterior side, the ravities of the cartilage containing the veins opening here into a common depression. The upper veins (vy) come from the region of the base of the tentacles; the lower veins (v’) come from the anterior portion of the funnel. In the central part of the cephalic process is a small cavity which extends nearly to its tip and communicates with the cavity containing the vein from the cephalic region. SUMMARY. It may be a convenience if the additions to our knowledge of the anatomy of Nautilus pompilius presented in the foregoing pages are briefly summarized. The principal result aimed at has been to unite the numerous isolated observations on Nautilus in a coherent account which will at least have the advantage of accessibility. It has been found that the digital tentacles have a regular arrangement, few variations from which exist. The nerve of each tentacle possesses accumulations of ganglion cells about its periphery corresponding to each of the annulations of the outer portion of the tentacle. The inner pro- jecting side of each segment of the digital tentacles is covered by a peculiar epithelium, which 194 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. there is some reason to consider as sensory. This portion of the segment is also provided with a peculiar musculature which enables it to act as an adhesive organ of considerable power. The evidence renders it probable that the lamellated organ upon the inferior labial lobe of the female is composed of a number of modified cirri. Between the lamelle are peculiar pits, lined by an epithelium which seems to be sensory. Vay per Horven’s organ of the male is shown to be the homologue of the inferior labial lobe of the female. Its lamelle correspond to the lamelle and cirri of the inferior labial lobe. Van per Horven’s organ is largely glandular; its activity may be periodic. Among the gland cells in all parts of the organ are scattered great numbers of sensory cells of a peculiar character. These seem to correspond to the sensory cells observed upon the inferior labial lobe of the female. It is to be noted, however, that in the latter organ the sensory cells are concentrated, hut in the former scattered. The inferior labial lobe is provided with a quite complex special musculature. A similar musculature is possessed by VAN DER HOEVEN’s organ. The second cirrus of the spadix bears a set of glands hitherto undescribed. The structure of the large slime gland upon the outer surface of the spadix sheath is described. A similar gland is found in a less developed condition upon the outer side of the sheath of the antispadix. The spadix possesses a powerful muscle, extending from its base across the cephalic sheath. The ocular tentacles are proven by their inneryation to be members of the digital series, modified for a sensory function. Upon the inner side of the nerve, within the ocular tentacles, is an acces- sory nerve composed of many bundles of nerve fibers, which enter the primary nerve as they pass toward the central nervous system. The ocular tentacles possess ** breaking planes,” i. e., planes where the tissues are somewhat discontinuous, and along which the tentacles break with great ease. Attention is called to the fact that the position of the organs of the pallial complex of Nautilus has been incorrectly figured and described by all authors except Joubin. The arrangement of these organs differs from that found in the Dibranchiata, and approaches that found in many Gastropoda. The gills, anus, preanal and interbranchial papille, pericardial and renal pores, and the nidamental gland are situated upon the inner surface of the mantle. The paired repro- ductive orifices are situated upon the body wall within the mantle cavity. There does not yet seem to be suflicient evidence to warrant our calling certain papille near the bases of the gills vsphradia. Both dissections and serial sections of the papille in question have failed to show the special innervation required; other observers also seem to be a little less than sure of the presence of special nerves to these papille. The funnel is composed of two essentially different portions, the anterior part being fibrous, the posterior portion muscular. The crura of the funnel are so formed that they can, by ¢ fanning motion, cause respiratory currents through the mantle chamber, and possibly currents strong enough for the progression of the animal. : The visceral portion of the body wall is thin and non-muscular. It contains a nervous plexus. It is attached to the shell by three aponeurotic bands proceeding from the ends of the shell muscles. The dorsal and posterior ventral bands limit the septum-forming portion of the body wall. A sharp backward projection of the dorsal aponeurotic band corresponds to a depression in the face of each septum in the younger half or two-thirds of the shell. Aside from minor additions in the description of the anatomy of the digestive tract as a whole, the muscles of the buccal mass are described and figured. They are found to forma quite highly developed system. The renal organs are found within the mantle and in the reverse position from that described by earlier authors. Willey’s sketches and my own dissections have been combined to form a nearly complete account of the arterial circulation. Some previously undescribed nerves have been followed to their terminations, especially the nerves of the ocular tentacles, of VAN DER Horven’s organ, and of the spadix and antispadix. The ocular nerves are branches of a nerve supplying digital tentacles as well. The nerves of Van per Horven’s organ correspond to the nerves of the inferior labial lobe in all particulars. The otoeystic nerve arises from the cerebral ganglion, BEB LIOGRAPH ¥- . AppELLOF, A. Die Schalen von Sepia, Spirula und Nautilus. Studien tiber den Bau und das Wachstum. Svenska Akad. Handl. Bd. xxv, No. 7,106 pp. 3 figures. 12 plates. . Barner, F. A. The Growth of Cephalopod Shells. Geol. Mag. Dee. 3. Vol. iv, pp. 446-49. 3 figures. . Barner, F. A. Professor Blake and Shell-growth in Cephalopoda. Ann. Mag. Nat. Hist. Vol. i, pp. 421-427. . Beynert, Grorcre. The Inhabitant of the Pearly Nautilus. London Medical Gazette. viii, p. 729. Figs. . Bennerr, G. Notes on the Range of some Species of Nautilus, on the Mode of Capture, and onthe Use made of them as an Article of Food. Proc. Zodl. Soc. London. Pt. 27, pp. 226-229. . Bennerr, G. Notes on the Pearly Nautilus. Ann. Mag. Nat. Mist. Ser. 4. Vol. xx, pp. 331-334. . Bennett, G. 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Mordhindlgr. skand Naturforsk. 6 Mote, pp. 243, 244. 1830. Quoy vr Gaimarp. Description d’un fragment de Mollusque inconnu, présumé étre celui du Nautile flambé (Nautilus pompilius Linn.). Tlustrated. Ann. Sci. Nat. Tome 20, pp. 470, 471. 1834. Quoy pr Gaimarp. Stiick eines unbekannten Weichthieres, wahrscheinlich yon Nautilus pompilius. Tlust. Isis. pp. 1146, 1147. 1843. Reeve, Lovety. History and Observations on the Pearly Nautilus, involving a new theory to account for the camerated construction of its shell by the aid of the siphonic membrane. Ann. Mag. Nat. Hist. Vol. xi, pp. 119-125. 1705. 1766. 1859. 1887. 1898. 1843. 1841. 1841. 1841. 1841. 1841. 1895. 1896. 1879. 1879. 1880. 1843. 1843. 1848. 1849. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. LOT Rumen, G. E. ‘‘ Nautilus major sive crassus’’ in his ‘‘Amboinsche Rariteitkammer.’’ Amsterdam. Fol., pp. 59-62. Pl. XVII. G, E. Rumpw’s Amboinische Raritiiten-Kammer yon Schnecken und Muscheln aus dem Holliindischen tibersetzt von P. L. St. Muller, vermehrt von J. H. Chemnitz. Auf Kosten, Johann Paul Kraus in Wienn. SaANDBERGER, G. Kurze Betrachtungen Uber Sipho und Siphonaldute, sowie tiber Eizelle und andere iiussere und innere Merkmale der Schaale des gemeinen Schiffbootes (Nautilus pompilius L.); nebst einigen Ver- gleichungen mit analogen Stticken der Gattungen: Clymenia, Goniatites u. Ammonites. 1 plate. 7. Bericht d. Oberhess. Ges. f. Natur. u. Heilk. pp. 75-80. Saito, Epcar A. Note on the Pearly Nautilus. Jowrn. Conch. London. Vol. v, pp. 226, 227. Srurany. Ueber ein Massengeschenk von Nautilus Exemplaren durch Dr. Zdekauer. Annalen des K. K. Naturhistorischen Hofmuseums. Bd. xiii, H. 4. Ueber Nautilus pompilius. (Abbildung mit Erklirung.) ror. N. Not. Bd. xxvi. No. 572. pp. 344, 345. VALENCIENNES, A. Nouvelles recherches sur le Nautile flambé. 4 plates. Archives du Muséum. Tome 2, pp. 257-314. VALENCIENNES, A. Nouvelles recherches anatomiques sur le Nautile (Nautilus pompilius). Compt. Rend. Acad. Se. Paris. Tome 12, pp. 174-179. VALENCIENNES, A. On the Anatomy of Nautilus. Ann. Nat. Hist. Vol. vii, pp. 241-245. VALENCIENNES, A. Ueber Nautilus pompilius. Fror. N. Not. Bd. xvii, No. 369, pp. 265, 266. VALENCIENNES, A. Untersuchungen des Thieres yon Nautilus pompilius. Berlin. Monatsber. pp. 55-58. Mier, Jon. Bemerkungen hierzu. Ibid. pp. 58, 59. VayssiereE, A. Sur le dimorphisme sexuel des Nautiles. Compt. Rend. Tome 120, pp. 1431-1434. Vayssiere, A. Etude sur l’organisation du Nautile (caractéres zodlogiques, dimorphisme sexuel, tentacules et spadice). 4 plates. Ann. Sei. Nat. 62° année. 8° sér., tome ii, pp. 137-183 (186). Vicetius, W.J. Bijdrage tot de Kennis van het excretorisch System der Cephalopoden. 2 plates. Academisch Proefschrift. Leiden. 8vo. 175 pp. ViceEtius, W. J. Over den bouw der nieren bij Cephalopoden. Tijdschr. Nederl. Dierk. Vereen. D. 4. 2. Afi. Versl. pp. lix—lxiii. Vicetius, W. J. Uber das Excretionssystem der Cephalopoden. 3 plates. Niederliindisches Arch. f. Zool. Bd. v, pp. 115-184. : Vrouk, W. Sur l’anatomie du Nautilus pompilius. L’ Institut, xi, No. 518, p. 414. Vrouk, W. On the Anatomy of the Pearly Nautilus. Ann. Nat. Hist. Vol. xii, pp. 173-175. Vroiik, W. Over het maaksel van den Nautilus pompilius. Aanteek. Utrecht. Genootsch. pp. 34, 35. Vrouk, W. Brief aan—J. J. Rochussen—over het ontleedkundig zamenstel van den Nautilus Pompilius. 2 plates. Tijdschr. voor de wis- en natuurk. Wetensch. D. 2, pp. 307-327. . Vrourk, W. Lettre sur quelques points de l’organisation de l’animal du Nautile flambé, addressée 4 M. Eudes- Deslongschamps. 1 plate. Caén. Hardel. 4to. 20 pp. Extrait du X® volume des mémoires de la Société Linnéenne de Normandie. . Witiey, ArrHurR. In the Home of the Nautilus. 2 figures. Nat. Se. London. Vol. vi, pp. 405-414. . Winey, Artaur. Letters from New Guinea on Nautilus and some other Organisms. Quart. Journ. Micr. Sci. Vol. xxxix, pp. 145-180. 24 figures. . Wittey, Artnur. On some Variations in the Shell of Nautilus, with Description of a new Variety (N. pom- 2 ilius, var. Moretoni, noy. var.). 3 figures. Quart. Journ. Mier. Sci. Vol. xxxix, pp. 227-231. ’ 2 tna} ? I . Wiuiey, ArtHur. The Preocular and Postocular Tentacles and Osphradia of Nautilus. 1 plate. Quart. Journ. Mier. Sci. Vol. xl, pp. 197-201. . Wiitey, Arrnur. The Adhesive Tentaclesof Nautilus, with some Notes on its Pericardium and Spermatophores. 1 plate. Quart. Journ. Mier. Sci. Vol. xl, pp. 207, 208 (209). . Wriitey, ArtHur. Ovyiposition of the Nautilus. 6 figures. Proc. Roy. Soc., London. Vol. 1x, pp. 467-471. . Wititey, Artaur. The Embryology of the Nautilus. 6 figures. (A reprint of the preceding article.) Nature. Vol. lv, pp. 402, 403. . WitLEy, ArTHUR. Some Zoological Results of a Voyage to Melanesia during the years 1894-1897. Proc. Cambridge Philosophical Society. Vol. ix. Part viii. pp. 398-401. g } q PI . Woopwarp, Henry. The Pearly Nautilus (pompilius). Cuttlefish and their Allies. Student und Intell. Obs. Vol. iv. Pt.1. 2 plates. pp. 1-14. Pt. 2. 2 plates. pp. 241-249. . Woopwarp, Henry. On the Structure of the Shell in the Pearly Nautilus. Report 40th Meet. Brit. Ass. Adv. Sci. (1869). pp. 125-129. . Wricut, THomas. Observations on Dr. Buckland’s Theory of the Action of the Siphuncle in the Pearly Nau- tilus. London and Edinb. Philos. Mag. N.s., vol, xii, pp. 503-508. PLATE, 1. lic. 1.—A Nautilius seen from the right side, the right half of the shell having been cut away. AY, anterior yentral aponeurotic band. C, cirrus of a digital tentacle. Osh, cephalic sheath, composed of the fused sheaths of digital tentacles, CR, crus of funnel. DM, dorsal portion of mantle. E, eye. I, funnel. Ho, hood. I, involution of shell. O’, preocular tentacle. O’’, postocular tentacle. PV, posterior ventral aponeurotic band. S, living chamber of shell. Si, siphon of shell. SI, siphuncle of body. SM, area of attachment of shell muscle. Sp, last-formed septum. YM, ventral portion of mantle. This is free from the body from the edge as far back as the anterior ventral aponeurotic band. 198 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM. PLATE |. = = ~ -By je} > fy N = my = 7A) L. ©. GRIFFIN, DEL. + PLATE II. Fic. 2.—View of the dorsal side of a Nautilus remoyed from its shell. OR, erescentic ridge on the posterior face of the hood, DA, dorsal aponeurotic band. DM, dorsal portion of mantle. The index line points to a depression in the dorsal side of the body into which fits the involution of the shell. DT’, second digital tentacle. BE, eye. HoA, auricle of hood. HoC, Ho, cirri of tentacles composing the hood. O’, preocular tentacle. Si, base of siphuncle. X, backwardly projecting point of dorsal aponeurotie band, which is evidently the cause of the small back- ward projections near the dorsal edges of the septa, shown in Fig. 1. y, constriction of the siphuncle where it passes through a septum. 200 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. Vill, 5TH MEM. PLATE ll. Ho. A MOEN &CO. BALTIMORE L. £. GRIFFIN, DEL. = a Se ® i 7 » Sar = - i i.) ' - . i : : A = s - ‘ i : ; i - . i 1 - . 7 , = és i i A ‘ A i a 7 : : bd : - i ny - ¢ . : w - 4 i - ‘ ns 1 aa + G 7 i : a = . ; - t : : an A = a , ; : : = - : : _ r ¢ i os v0 ; i= 5 i O) 1: > “S - fy : ad , a ; 5 . : 1 Y A 7 o , i mrs a) : i i = ’ i ie = i ; - j 1 4 J —— ‘4a a y = 7 } 5 : = i i - h PLATE il. Fic. 3.—Male viewed from the ventral surface; the mantle has been turned back over the posterior end of the body, exposing its inner surface and the organs contained in the mantle chamber. A, anus. DT, digital tentacles, composing the cephalic sheath. E, eye. F, funnel. IP, interbranchial papilla. O”, postocular tentacle. P, penis. PA, preanal papillee. PP, pericardial pore. RA, anterior renal pore. RP, posterior renal pore. 202 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. Vill, 5TH MEM. PLATE Ill. — ———d) AHOEW 8CO. BALTIMORE L. £. GRIFFIN, DEL. PICAWE: TV: Fic. 4.—Mantle chamber of female viewed from the ventral side. The mantle has been turned back over the posterior end of the body. B, raised and overlapping border of the nidamental gland. BV, branchial vein of the anterior gill. F, base of funnel. GA, anterior gill. GP, posterior gill. LM, lateral portion of mantle. N, nidamental gland. OV, protruding end of oviduct; ovidueal papilla. PA, preanal papillee. SM, shell muscle. VM, ventral portion of mantle. Y, thickened portion of mantle between the inturned ends of the nidamental gland. Fig. 5,—Cephalic region of female viewed from the dorsal side. The hood has been slit open along the median line to show the arrangement of the labial lobesand tentacles. B, buccal mass. CR, crescentic ridge upon the posterior face of the hood. DM, dorsal portion of the mantle. Ho, hood. L, lamellated organ upon the center of the inferior labial lobe. The fan-like cirrus-bearing portions of the lobe are seen at the sides of the lamellated organ. SLL, superior labial lobe. KG. 6.—-Funnel, opened and viewed from the ventral side. C, infundibular portions of the cartilage showing through the integument of the dorsal wall of the funnel. OR, crus of funnel. L, ligamentous band of the integument extending from the posterior edge of the funnel backward over the surface of the shell muscle. M, shell muscle, V, valve of funnel 204 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM. PLATE IV - ~~. VM L. £. GRIFFIN, DEL. gee ees . PLATE V. Fic. 7.—Male, viewed from the dorsal surface. The hood, mantle, and body wall have been cut open in the median line in order to show the mouth parts, the hzemoceel, and the ccelom, with their contained organs. Ao, aorta. ASp, antispadix. B, buccal mass. BM, buccal membrane, cut open dorsally to show the tips of the jaws. BW, wall of the posterior px wrtion of the body. OR, crescentie ridge upon the posterior face of the hood. DBR, dorsal buceal retractor muscle. DM, dorsal portion of the mantle cut open and folded down. DT, digital tentacles. GL, genital ligament. Ho, hood. L, L, lobes of the liver, covered by the heemocalic membrane. Oe, esophagus, lying in the heemoccel. - S, siphunele. SLL, superior labial lobe. Sp, spadix. St, stomach. T, testis. UJ, upper jaw. VM, ventral portion of mantle. X, junction of the hzemoccelic membrane and body wall along the line of the dorsal aponeurotic band. 206 5 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM. pa L. £. GRIFFIN, DEL. Sp SLL.-- DT UJ. DBR Oe VM BW PLATE V. AHOEW ACO BALTIMORE PLATE VI. Fic. 8.—Ventral view of Van der Hoeven’s organ. >< 2. L, vertical laminze. N, nerve. VF, vertical fissure. W, wall of the pocket, or atrium, into which the anterior end of the organ projects cut from its attachment to the organ and folded to one side. 1, 2, 3, muscles of the organ. Fic. 9.—Longitudinal section of Van der Hoeyen’s organ, taken through the median vertical fissure. (The ventral side is uppermost.) 2. G, G, glandular portion of the organ. HF, horizontal fissure. L, horizontal lamin. Fic. 10.—Cross section of Van der Hoeven’s organ taken just back of the middle of the organ. (The ventral side is uppermost.) > 2. Fie. 11.—Shell of Nautilus pompilius. % natural size. 208 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII], 5TH MEM. PLATE VI. VF Kivey Y, igh Jb fbi Deby Tih) THM ELITR H If ROGEN ACO BAETIMOR L. E. GRIFFIN, DEL. Fr Fia. Fic. Fra. Fia. Pia. Fi. Fic. Fia. Fia. Fia. Fia. Fic. BIGse2e Fic. PLATE VIL +. 12.—Antispadix, viewed from the outer side. Nearly twice natural size. G, slime gland upon the sheath of the antispadix. F, projecting flap of the sheath, partly covering the fourth tentacle. 4, fourth tentacle. 13.—Spadix, viewed from the inner side. The loose integument covering its base has been cut away. Natural size. 1, first cirrus. 2, second cirrus. 3, third cirrus. ? 14.—Spadix, viewed from the outer side. Natural size. G, slime gland of the sheath. SH, line along which the integument has been cut away to expose the base of the spadix. 1, first cirrus. 2, second cirrus. 3, third cirrus. 4, fourth cirrus, nearly covered by the projecting flap of the spadix sheath. 15.—First cirrus of the spadix. Nearly natural size. 16.—Second cirrus of the spadix, viewed from the ventral side. Natural size. 17.—Third cirrus of the spadix, viewed from the dorsal side. Natural size. 18.—Third cirrus of the spadix, viewed from the ventral side. Natural size. 19.—Fourth cirrus of the spadix. Natural size. 20.—Lamellated organ upon the median portion of the inferior labial lobe of the female, viewed from the dorsal side. Twice natural size. 21.—Rhinophore, viewed from the anterior side. > 3. DP, aperture of the dorsal pit. . F, aperture of the fossa. 22.—Longitudinal section of the rhinophore passing through the fossa and the tentacle. a, nerve. b, c, portions of the fossa. c is near the opening of the fossa to the exterior. The section does not extend to the closed central end of the fossa. The heavy outer line indicates the extent of the external epithelium. Only as much of the rhinophore as is hounded by this line extends beyond the surface of the body. 23.—Cross section through the middle of a gill. x 2. 1, branchial vein. 2, branchial artery. 3, stem of gill. 4, respiratory membrane of leaflet. 5, supporting portion of leaflet. 24,—Lamellated region upon the inner surface of the cephalic sheath of the female, just back of the ventral notch, which forms an organ for receiving the spermatophore. Below the lamellated region the tip of the funnel is seen; at the sides, some of the most ventral digital tentacles. Twice natural size. —Spermatophore iz situ upon the lamellated receiving region. Natural size. 26.—Base of the inferior labial lobe of the female, seen from the dorsal side. X 2. 1, 1’, levator muscles. 2, 2’, approximator muscles. 3, 4, 3%, 4’, lateral retractor muscles. 5, dorsal median retractor muscle. 210 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM. PLATE Vil. L. €. GRIFFIN, DEL. Vol. 8—No. 5 8 PLATE VIII. Fic. 27.—Dorsal view of the digestive organs. Natural size. Ao, dorsal aorta, dividing into innominate and buccal arteries. B, buccal mass. C, C, posterior columellar arteries. Coe, coecum. GL, gastric ligament. H, hepatic artery. I’, first loop of the intestine around the ececum. I’, posteriorly directed portion of the second loop of the intestine. I’, anteriorly directed portion of the second loop of the intestine. TA, intestinal artery. IL, intestinal ligament. L, L, left lobes of the liver. L’, L’, right lobes of the liver. Oe, cesophagus (proventriculus). PA, anterior proventricular artery. PN, PN, pallio-nuchal arteries. PP, posterior proventricular artery. St, stomach. Fic. 28.—Dorsal view of the buccal mass, the buccal membrane and enveloping muscular membrane being cut in the median dorsal line and opened. X 2. Ao, aorta, dividing into innominate and buccal arteries. BM, buccal membrane. CG, cerebral ganglion, giving off nerves to the buccal mass. DLR, dorso-lateral buccal retractor muscles. DR, dorsal buccal retractor muscle. LJ, tip of lower jaw. LJ’, posterior portion of the outer flange of the lower jaw. LM, levator muscle of the buccal mass. M, mandibular muscle. MM, enveloping muscular membrane. N, nerves to the buccal membrane. Oe, cesophagus. UJ, upper jaw. X, buecal membrane, passing onto the base of the superior labial lobe. Fic. 29.—The buccal mass turned upward and backward so as to show its ventral surface and the dorsal surface of Van der Hoeven’s organ. Natural size. Fig. 30.—Side view of the upper jaw. & 2. Fic. 31.—View of the inner surface of half of the lower jaw, cut in order to show the small inner flange. X 2. 212 PLATE Vili. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM, = ILM. Fig. 29. Fig. 30. upper jaw. Vf srnasiess ESO Fig. 31. “= St © BALTIMOR L. £. GRIFFIN, DEL. ‘ = ‘ , “ais by 1 : . r ‘ ee : 4 E } i ‘ 4 f Rey) ’ : nf a A ? 4 f i h ) ’ i N , , ‘ i F ‘ t - + 32.—Alimentary canal opened along the dorsal side. Natural size. AP, anterior prelingual process. — BM, buceal membrane. C, cecum, showing its projecting lamelle. : 7 HD, openings of the hepatic ducts into the coscum. ; LJ, lower jaw. | MM, mandibular muscle. Oe, cesophagus. PP, posterior prelingual process. : Pr, proventriculus. R, radula. Re, rectum. 8, saccular posterior portion of the stomach. : SO, salivary pore. SP, salivary process. Tn, tongue. UJ, upper jaw. V, vestibule. 1,1, intestinal ridge. 2, intestinal ridge. 3,3, intestinal ridge. 4, foliaceous ridge. ; : ; Fig. 33.—Ventral yiew of the buccal mass, a portion of its muscular membrane having been folded back. BG, buccal ganglion. 4 a BM, buccal membrane, cut and turned forward oyer the tip of the jaw. LJ, outer flange of the lower jaw. LM, levator muscle ofthe buccal mass. ~M, mandibular muscle; this ends ventrally along the edge of the upper jaw. MM, muscular membrane of the buccal mass. N}, outer cerebro-buccal connective. N®#, inner cerebro-buccal connective. ara. Ph. G, pharyngeal ganglion. RL, ligament of the radular sac. : 2 VBR, ventral bueeal retractor muscle. LJ, tip of lower jaw. M, mandibular muscle. MM, muscular membrane of the buccal mass. UJ, tip of the upper jaw. UJ’, posterior edge of the inner flange of the upper jaw. Fic, 35.—The radular sac and the lingual muscles of one side exposed and viewed from the ventral side. X 2. EL, external lingtal muscle. 7 - IL, internal lingual muscle. LP, lingual protractor muscle. R, radular muscle. R/ cut end of the radular muscle. Ra, radula. E RS, radular sae. T, tendinous area where the lingual muscles join. X, division of the septum. : ; Y, point of the upper jaw to which the lingual protractor is attached. PLATE IX. T, tentacles of the stomach. é X, apparently permanent ridges of the cesophagus. F Oe. M, membrane surrounding the base of the wsophagus and connecting with the membrane surroun the central nervous system. , = OM, part of the membrane stretched between the ventral buccal retractors. RS, radular sac. ee 3 retractor of the anterior prelingual process. retractor of the posterior prelingual process. 3, unpaired muscle, forked posteriorly, going to the posterior prelingual process. ; muscle extending into the posterior prelingual process, and also to the portion of the tongue anterior to upwardly directed part of the radular sac. muscle to the anterior portion of the tongue. muscle to the membrane covering the projection of the upper jaw. muscle to the dorsal surface of the radular sac. Muscle which probably plays a share, at least, in the opening of the jaws. origins of muscles 1, 2, 7, upon the inner surface of the muscular membrane. ee —Dorsal view of the buccai mass, the enveloping muscular membrane haying been cut along the median line. The view is also somewhat from behind. 2. oo % A, branches of the superior mandibular artery penetrating the mandibular muscles. BM, buccal membrane, also slit open dorsally. : % a Oe, wsophagus, swollen at one place by food which remained in it when the animal died. EL/, cut end of the external lingual muscle. . = S, septum: extending from the dorsal median line of the tongue to the muscular membrane just above the radular sac, which has been cut away from the exposed side of the preparation, oy 214 ; MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM PLATE Ix. \ RS_----- BM eee Ser Fig. 32. L. £. GRIFFIN, DEL. MM____ \ \ \ RS____- VBR Oe. M BM Fig 33. LI OM Us MM « ' i te) ~ : : . : ' , . ‘ . = . : « ' ri i ag 1 u ak is i : J f : i 7 : An poy . , } { . 4 i 1 y a t i i 1 1 - ‘ ' fi t . & : 5 Ww i . t w 5 : ,, AP as i C 7 ‘a uu ‘ , ‘ * r . PLATE X. Fic. 36.—The ventral portion of the body wall is cut open and reflected to show the pericardial chamber. Natural size. a. br. v., anterior branchial vein; in this case collapsed and not forming an auricular expansion. a. p.g., anterior pericardial gland. The one to the left lies naturally; the one on the right has been turned upward to show the anterior branchial vein. H, heart, enfolded by the pallio-visceral ligament. The septal artery runs over its ventral surface, suspended by a mesentery-like fold of the pallio-viseeral ligament, and through the posterior yiseero-pericardial aperture. j, junction of the body wall and the pallio-visceral ligament posteriorly. 1, ligament from the ventral edge of the posterior renal sac extending along the body wall. p. a., pallial artery. p. br. v., posterior branchial vein, partly expanded. p- p-g., posterior pericardial gland. p. v.a. b., posterior ventral aponeurotic band. p. v.L., pallio-visceral ligament. The three apertures through it by which the pericardial and genital divisions of the ccelom are put in communication are at either side of and behind the heart. p. V-p.ap., posterior viscero-pericardial aperture. pyr. s., pyriform sac. r.s., anterior wall of the right posterior renal sac. Fig. 37.—Renal appendages from the posterior wall of one of the renal sacs. 2. Fig. 38.—Male genital organs viewed from aboye and in front. The anterior portion is represented as dissected from the body wall. Natural size. ac. gl., accessory gland surrounding the vas deferens. ao, aorta, passing upward from the heart at the back of the heemoccelic membrane- g.1., genital ligament. gas. |., gastric ligament. I, intestine, cut at the middle of the second loop. Tl., intestinal ligament. P. ap., external opening of the penis. P.1., left tube of the penis. P.r., right tube of the penis. p-v- L., pallio-visceral ligament at its attachment to the posterior side of the heart. pyr. ap., external aperture of the pyriform sac. pyr. s., pyriform sac. r., rectum. sep., septum dividing the spermatophore sac. sp. s., spermatophore sae. §S. V., seminal vesicle. ae : T. ap., aperture of testis. T.g., face of the testis which is pressed against the stomach. T. 1., face of the testis which is pressed against the liver. y. d.!, proximal thin-walled portion of the vas deferens. y. d.2, commencement of the thick-walled portion of the vas deferens, which extends from this point to the seminal vesicle. x, thickening of the tissues of the genital ligament extending from the root of the siphuncle. y, tunic of the accessor ind carried upon the back of the testis. Fic. 39.—Female genital organs viewed from in front and aboye. The anterior portion of the ovary rests upon the pallio-visceral ligament. The heart and auricles show through the yiscero-pericardial apertures. Natural size. ao, aorta. ex. ap., external aperture of the oviduct. g. |., attachment of the genital ligament to the posterior body wall. gas. |., gastric ligament. I, intestine. I.]., intestinal ligament. la., line along which the heemoccelic membrane is attached ventrally. l. y-p. ap., left anterior viscero-pericardial aperture, Ov., ovary. | Oy. ap., aperture of the ovary slightly pulled away from the inner aperture of the oviduct. ovid., thin-walled portion of the oviduct. ovid. ap., inner aperture of the oviduct. ovid. pap., plaited, freely projecting tip of the oviduct; the oviducal papilla. p- au., posterior auricle. pyr. ap., opening of the pyriform sac into the mantle cavity. pyr. s., pyriform sae. . rl, ligament attaching the rectum to the pallio-visceral ligament. r. V-p. ap., right anterior viscero-pericardial aperture, s, nodule in the genital ligament at the root of the siphunele. Fic. 40.—Cartilage viewed from the anterior side. Natural size. c., cephalic process. i., infundibular process. 1. i., point of attachment of the levator of the funnel. m. p., median process of the body of the cartilage. v, Vv’, holes through the cartilage occupied by veins. 216 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM. PLATE X. Gl as I __ gas. ft. Ov. ENS Ov. ap T. ovid. ap pyr. s i z= rl ouid...__= \ a T. V-p. ap. B cpus | 7 p. au v. ovid. pap.- is =. 1 } _l. v-p. ap. ex. ap.- == o+----pyr. ap. la. eRe Laps L. £. GRIFFIN, DEL. 7 : i 7 os a - 7 4 =3) , = — w- i oa . MI ' 4 r] ( tes a ra : 7 7 2 + 3 - caf B) >» “a oe ee s - 4 s y 7 _ - j e ‘ a” a ao 7 re 7 =4 : | « » yu . 4 7 + .) ’ i A : PLATE XI. Fic. +1.—Nervous system, dissected and viewed from the dorsal side. 2. nerve to mandibular muscle. pharyngeal commissure. nerves to mandibular muscle. . pharyngeal ganglion. outer cerebro-buccal connective. inner cerebro-buceal connective. right nerve of the inferior labial lobe. infundibular nerve. nerves to digital and superior labial tentacles. large nerve innervating hood and digital tentacles. nerye of postocular tentacle; the other branch of this nerve innervates the preocular tentacle and the posterior portion of the hood, and sometimes digital tentacles. cerebral ganglion. - pleuro-visceral ganglion. neryes to shell muscle and the body wail. nerve to the walls of the vena caya, in this case springing from the visceral nerve, 22. Nerves to the spermatophore sac and the genital duct. , herve seeming to go to the posterior wall of the anterior renal sac. nerve seeming to go to the posterior wall of the posterior renal sac. posterior branchial nerve. anterior branchial nerve. nerve to the wall of the vena caya, in this case arising directly from the pleuro-visceral ganglion. visceral nerve. nerves from the outer end of the cerebral ganglion to the posterior portion of the hood. base of the optic nerve, which may be a ganglion. portion of the optic nerve in the stalk of the eye. branches of the optic nerve in the capsule of the eye. nerves proceeding from the cerebral ganglion to the dorsal side of the buccal mass, some being distributed to the mandibular muscles, but most passing to the papillee on the edge of the buccal membrane. pedal ganglion. pedal commissure. herye proceeding to the base of the spadix, and there ending in an enlargement from which several fine nerves go to the tissues of the spadix. nerve to cesophagus. buccal ganglion. buccal commissure. nerve to salivary gland. , ganglion of inferior labial lobe (or Van der Hoeyen’s organ) 218 = MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VIII, 5TH MEM. PLATE XI. L. £. GRIFFIN, DEL. - n 5 a : ' 14 1 Todt 5 . 1 . . p ‘ / i ' + Or y | F . : < . 2 , 1 , “4 om, ' ‘ . ry ‘ . i 4 . ; 5 : - ; . rd - ’ yi F i a i x es a , 6 io 7 ‘ rr if . Pers 5 “7 = ‘i : " : } : - i q (i 7 i ’ ; ; P i >! 7 _ 6 , - A ‘ 5 ey . » A Ke) oi 7 * : - . 9 7 al . oe ' ’ wis i . wa ‘ ee Py) - Fae ee Wy t os FL 7 y . Fn at . ie ‘in , : ae , a td Same ! PLATE XII. 42.—Central tooth of the radula. 43.—First lateral tooth of the radula. 44.—Second lateral tooth of the radula. _ 45.—Third lateral tooth of the radula. . 46.—Fourth lateral tooth of the radula. . 47.—Fitth lateral tooth of the radula. ;. 48.—Sixth lateral tooth of the radula. . 49.—Cross section of a digital tentacle. C. L. x 15. ©, cirrus. SH, sheath. ;. 50.—Longitudinal section of the tip of a digital tentacle. C. 1. 20. A, artery. G, G, annular grooves between ridges. LM, fasciculi of longitudinal muscles. N, nerve. R, suctorial ridge. SH, tip of sheath of cirrus. T, transverse muscle layer. V, vein. 220 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, VOL. VII], 5TH MEM. L. £. GRIFFIN, DEL. PLATE XIl. A MOEN ACO BALTIMOKE PLATE XIII. Fic. 51.—Cross section of a cirrus of the superior labial gronp ofamale. C. lL. > 20. A, artery. ; S CM, circular muscle layer. h, thickened epithelium of the inner (suctorial) surface ee the annular ridge. LM, radially arranged longitudinal muscles. LM’, outer layer of longitudinal muscles. N, nerye. OM, oblique muscle layer. RM, radiating transverse muscle fibres inside the projecting portion of the annular ridge. 7 F le TM, transverse muscle fibres surrounding the nerve and radiating outward between the longitudinal muscles, V, vein. a ; Fig. 52. Si paeicdial section of the tip of the first cirrus of the spadix. Cae es N, nerve: T™, alternating layers of transverse muscle fibres. V, vascular corium of the tip of the cirrus. Fig. 53.—Cross section of the first cirrus of the spadix. C. L. > 7. A, artery. N, nerve. V, V, veins. Fig. 54.—Cross section of the fourth cirrus of the spadix. C. L. & 14. Fig. 55.—Longitudinal section of a gland of the second cirrus of the spadix. C. 1. x 60. 1, epithelium of the dorsal surface of the cirrus. G, secretory epithelium. L, lumen of gland. N, neck of gland. : 222 : an Memoirs of the National Academy of Seiences, Vol. VILL, 5th Mem. PLATE XIII. Fig. 54 Fie. 53 L. E. Griffin, Del. Fic. Fig. Fig. Fic. Fia. PEATE Pe Xiy 56.—Slightly oblique cross section of the second cirrus of the spadix. C. lL. > 12. A, artery. G, gland. GL, layer of glands. N, nerve. V, vein. 57.—Section through the slime gland on the sheath of the spadix perpendicular to the surface. C. L. x 20. A, a single cell of the glandular epithelium highly magnified. Camera lucida outline. Magnification about 400 diameters. 58.—Longitudinal section of the tip of the fourth cirrus of the spadix. C. L. x 10. N, nerve. V, vascular sinuses of the body of the cirrus. V’, vascular sinuses in the ridges upon the outer side of the cirrus. 59.—Slightly oblique cross section of the third cirrus of the spadix. C. lL. & 14. A, artery. Cr, crypt, with projecting tongue. By following the series of sections shown by each row of crypts the manner in which the tongue projects from the wall of the crypt may be made out. CrL, layer of crypts. V, vein. 60.—Longitudinal section of the tip of the third cirrus of the spadix. C. L. X58. Cr, crypt. N, nerve. 224 PLaTe XIV. [! Say eee ines ia rae ae apnea jae Fic. 60 Sciences, Vol. VIIT, 5th Mem. Memoirs of the National Academy of Fic. 56 CeL Fie. 59 , Del. iriffin E. ¢ L. PLATE XV. Mic. 61.—Longitudinal section of the tip of the second cirrus of the spadix. C.L. x 14. G, gland. N, nerye. hic, 62.—Longitudinal section through a crypt and its tongue of the third cirrus of the spadix. C.L. X 35. ric. 63.—Longitudinal section of the base of the preocular tentacle. C.L. > 20. N, nerve trunk. N’, nerve bundles running along the anterior side of the nerve trunk. Fic. 64.—Longitudinal section of the tip of the preocular tentacle. C. L. x 20. A, artery. CG, ciliated groove on anterior side. G, groove on posterior side. N, nerve. n, branch nerye to the peripheral portion of the tentacle. R, ridge on anterior side of tentacle. V, vein. X, breaking plane. Fic. 65.—Slightly oblique cross section of the preocular tentacle about 6 millimeters from its tip. C.L. x 35. CG, ciliated groove between the upper and lower projecting ridges, R and R/. N, nerve. N’, nerve bundles running along anterior side of nerve. R, base of projecting ridge. V, upwardly projecting portion of the next lower ridge. 226 As, - Memoirs of the National Academy of Sciences, Vol. VIL, 5th Mem. PLATE XV. Fie. 65 RN WANS: Canny "vig FN G Mi . ¥ : WA Ny A! Y Y) Lj Lt CG aq Lp Se LATS My, Z > % St ‘FB Fs ASRS t @ z Fic. 64 Fie. 6] Fie. 63 L, E. Griffin, Del. Vol. S—No. 5——9 PLATE XVI. Fic. 66.—Cross section through the middle of Van der Heeyen’s organ. ©. L. xX 8. D, dorsal surface. A, atrium. G, G, G, glandular portions of the organ. Gn, ganglion. HF, horizontal fissure. L, laminze. N, nerves to the lamin. SH, wall of the atrium. VF, vertical fissure. Fic. 67.—Longitudinal section of a gland of Van der Heeven’s organ. ©. L. > 35 lic. 68.—Cross section of gland tubules of Van der Heeven’s organ. C. L. & 35. Fic. 69.—Section of the mantle through the bases of the preanal papillie. C. LL. x 12 G, G, glands. IM, inner surface of mantle. QO, opening of gland. OM, outer surface of mantle. P, P, bases of the preanal papille. Fic. 70. —Cross section of the salivary gland. ©. L. x 20. A, artery. BS, blood sinus of salivary process. N, nerve. O, opening from the central cavity of the gland to the pharyngeal cavity. 99¢ Memoirs of the National Academy of Sciences, Vol. VIII, 5th Mem. PLATE XVI. il Tints Ve qn I 1 1 I 1 ! Ny ” ‘QT QA rs > J D> ba NY, SZ) Oy ee = Site A Wee DB. S AGP A ZZ {re Yi Bon A Kod? MN ie Uk BUSS GS 1 \ Se O EAS NS a Oe ° OL Shwe ml Sa Se a ar ee Q Ny m—< >, Ss 1B Zoe, §=SNumN -' Se 7, AS SN S| ES ES Sed igs’ SA S7BXx — RRs = Gill \ Ul ys et > Q Fie. 70 L. E. Griffin, Del. 7 + Wy PLATE XVII. Fic. 71.—Cross section of the nerve of a digital tentacle. Borax carmine and Lyons blue stain. The ganglion cells in red. Fic. 72.—Epithelium of the inner side of an annular ridge of a digital tentacle. Also two isolated epithelial cells from the inner surface of the ridge. Fic. 73.—Section of the secretory epithelium from a gland of Van der Heeyen’s organ. The secretory cells had sep- arated from the submucosa, revealing the sensory cells which lie between them. As the section was somewhat oblique, the outer ends of the cells are not shown. + 230 O PLATE XVII. L. £. GRIFFIN, DEL. AOE 8 CO, BALTIMORE Mc DP Is 44-4 ». ) > —< Pd > DV - » D> DP , =: WD) D> yp ‘Prp» DD »>Prp? 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