Natural History Review/Series 2/Volume 1/Number 4/On Certain Points in the Anatomy and Physiology of the Dibranchiate Cephalopoda
[Read at the Meeting of the British Association, September, 1861.]
I propose, on the present occasion, to give some results at which I have arrived respecting the anatomy and physiology of the Dibranchiate Cephalopods; whose structure I have been engaged investigating for some time past. My observations will be confined almost entirely, to the so-called water system and to the blood system; and on these points I shall speak as concisely as possible, reserving for some future opportunity detailed accounts of them, when I hope to be able to lay before those interested in such subjects a memoir treating on the general anatomy of this order of the Cephalopoda.
First, then, with regard to the so-called water system. In the Octopodidæ this consists of five chambers; namely, two large chambers, containing the venæ cavæ; two small lateral ones, which open into the above, and which communicate by long slender tubes with the fifth, the posterior or "genital chamber," which always contains the special genital organ, the ovary or testis, according to the sex.
The two first-mentioned chambers lie along each side of the median line, separated by a membranous partition, and immediately within the abdominal wall. The liver lies in front of, and above, the ovary or testis behind them. Each opens into the branchial chamber by a nipple-shaped orifice placed near to the root of the gill. These two chambers contain the two venæ cavæ, with their glandular appendages. The convoluted or upper portion of the intestine, and a limited portion of the branchial hearts, also project into these cavities. Over all these organs the membranous wall of the chamber is reflected; but on the glandular appendages of the venæ cavæ if is scarcely, if at all, demonstrable. I shall uniformly designate these the "renal chambers," as they always contain the venæ cavæ with their glandular appendages, which latter undoubtedly perform, in whole or in part, the function of a kidney, as is now generally admitted.
Besides the external nipple-shaped openings already specified, there are other two orifices leading into these chambers. Those orifices are situated in the dorsal wall of the chamber, close to the base of the nipple-shaped orifices; and establish a communication between the renal chambers and two small, elongated cavities placed between the wall of the former and the lateral walls of the abdomen. These orifices are also somewhat nipple-formed, with the lips opening outwardly, or into the renal chambers, and are placed at the anterior extremity of the small chambers; the other extremity, which is some- what enlarged, abuts upon the branchial heart, and encloses within it the so-called "fleshy appendage" attached to that blood-propelling organ. The interior of these small chambers is longitudinally and irregularly laminated, with the surface of a glandular appearance, and a long, delicate tube connects each with the chamber containing the genital organ.
The genital chamber contains only the genital organ, whether ovary or testis, which is attached to the anterior wall of the chamber; the wall being reflected over the organ, as is clearly seen at the point of attachment. The membranous wall, however, very soon becomes so completely incorporated with the organ as to be no longer demonstrable. In the female, there are two ovarian outlets from this chamber, as well as the two already noticed as communicating with the small lateral chambers. In the male, there are three outlets only, two leading to the same small lateral chambers, and one into the vas deferens.
Thus it appears that all these so-called aquiferous chambers open externally, through the nipple-formed orifices situated in the branchial chamber. But, as might be expected, they have no direct communication with the blood system; at least, I have hitherto failed to discover any.
In the Loliginidæ we find these chambers considerably modified, and reduced to two in number, — the renal and genital. The former is no longer divided into two by a longitudinal median septum, but forms one large continuous cavity — the pericardial of most writers ; though it never contains the heart, so far as I have observed. In this group, however, it holds, in addition to the vense cavse and their glandular appendages, the hepatic ducts, with their attached pancreatic glands. This is the case in Loligo sagittata, L. media, Onychoteuthis Lichtensteinii, Sepia officinalis, Sepiola Rondeletii, and Ommastrephes todariis. In this last, the lower portion of the intestine and the greater part of the ink-bag, and in Sepia, one half of the stomach and the whole of the spiral cæcum, are also lodged within this chamber. And, in all the species, a small portion of the branchial hearts likewise protrudes a little into it. The nipples, which bring this chamber into communication with the branchial chamber, are placed further forward than in the Octopodidæ.
The genital chamber is very much increased in dimensions in this group, occupying the whole of the abdomen from the liver backwards to the end of the tail. It contains, besides the testis or ovary, with the single exception above alluded to, the stomach and cæcum; also the branchial hearts and their appendages, a small portion of the hearts only protruding into the renal chamber, as already noticed. The latter organs are placed in two recesses, situated at the sides towards the anterior end of the cavity, and which communicate freely with the chamber.
All these organs are covered with the membrane forming the wall of the chamber, which is reflected over them in the manner of a peritoneum; but it is not easily demonstrable, except at the points where the various organs are attached to the wall, and there it is always seen doubling back upon them. It is thus distinctly visible on the stomach, over which it passes backwards, forming a fold carrying the blood-vessels and nerves, which fold unites this viscus to the anterior extremity of the genital organ. The latter is also attached to the posterior extremity of the chamber by the same membrane in Ommaastrephes and Loligo; but in Sepia and Sepiola this extremity is free.
There are two oviducts in Ommastrephes; all the other species that I have dissected have only one, which is situated on the right side. They open through the lateral walls of the chamber, and lie apparently, between these walls and that forming the boundary of the abdomen, The male intromittent organ, which is always single, is situated on the right side, and the vas deferens communicates with the chamber by a small orifice opening through the wall of the same side.
Besides the genital outlets, there are other two. as in the Octopodidæ, which bring this chamber into communication with the venal cavity. Here, however, in the place of long, fine, duct-like tubes, there are short, wide, flattened channels, which pass from the sides of the chamber in front, and dipping downwards and forwards, between the wall of the body and that of the renal chamber, open into the latter immediately behind the nipples that communicate with the branchial chamber. These channels, which open into the renal chamber by slit-formed orifices, remind us of the manner in which the ureters open into the bladder in the higher animals.
There can be no doubt that the genital chambers in the two groups are homologous. The feet that, in both, they always contain the special genital organ—that the excretory channels of these organs always open into them in the same manner—and that they are always in communication with the renal chamber, sufficiently establishes this relationship.
The two additional, small, lateral chambers in the Octopodidæ are nothing more than enlargements on the channels of communication between the two chambers. Indeed, the chamber in the Loliginidæ differs from that in the Octopodidæ chiefly in the fact, that the former contains, in addition to the special genital organ, the stomach and cæcum; these organs, in the latter, being placed in what M. Edwards, in the "Voyage en Sicile," première partie, p. 123, designates the visceral or abdominal chamber; which in the Loliginidæ is either wholly or in part wanting. These digestive organs are therefore developed backwards, and are consequently thrust, as it were, into the genital chamber, bulging in its anterior wall, which becomes reflected over them in the manner we have seen.
The true nature of these chambers is a matter of no little interest. We have seen nothing to warrant the idea that they are directly connected with the vascular system, and certainly nothing to prove that they are for the purpose of receiving water from the exterior; but rather, on the contrary, that they form part of an apparatus for ejecting from the system the effete, nitrogenous, or urinary matters, and along with them the redundant fluids. But we must reserve further remarks on this subject until we have taken a glance at the vascular system.
According to Milne Edwards, the blood system in these animals is incomplete, as it is in all other mollusks. And in proof of this, a large sinus, or lacune, is referred to in the Octopodidæ, which is asserted to be the homologue of the abdominal or visceral chamber usually observed in the Mollusca. This sinus is situated on the dorsal region of the body, and extends nearly the whole length of the animal. It is divided by constrictions into three compartments; the anterior, or buccal, the median, or œsophageal, and the posterior, or gastric. With the exception of the anterior portion, which lies in the midst of the fleshy mass forming the base of the arms, this compound sinus is placed between the liver and the wall of the body. The posterior division communicates with the median portion by an orifice, not much wider than is sufficient to allow of the easy passage of the lower extremity of the œsophagus, or crop. It contains the gizzard, the spiral stomach or cæcum, and the hepatic ducts. The gastric organs are suspended in the centre of this chamber by a sort of mesentery, which is perforated, so as to allow the free circulation of the blood which flows in this great sinus. The median division holds within it part of the œsophagus, the crop, the posterior salivary glands, and the aortic trunk. It is much and suddenly constricted in front, on its passage through the nervous collar to join the anterior, or buccal division, within which are found the anterior portion of the œsophagus, the buccal organ, and the anterior salivary glands.
The whole of this great sinus is lined throughout by a membrane, the peritoneal membrane of Milne Edwards, which is reflected upon all the organs it contains; and the mesentery, before alluded to, is formed by a duplicature of this same membrane. It is also seen distinctly forming a sheath to the aorta, which floats freely in the centre of the cavity, and it can be readily traced on all the organs, though it is for the most part incorporated with their tissues, so as to be scarcely, if at all, discernible.
Three branches from the venæ cavæ open into this great blood sinus; two into the posterior, and one into the median portion. The latter opens on the right side of the œsophagus, behind and close to the point where the aorta enters the chamber.
Now, the lining membrane of the sinus is continuous with that forming the wall of these trunk veins: and it is almost impossible to resist the conclusion that the great sinus results from the expansion and fusion of these venous trunks. Indeed, I should have been much inclined to adopt Delle Chiaje's conclusion, alluded to by Milne Edwards, that this is a veritable venous sinus, even had nothing else turned up to elucidate this interesting point: we have evidence, however, which appears sufficient to set this matter at rest.
Milne Edwards says that in the Calmars, or those Cephalopods with ten tentacles, the abdominal sinus has entirely disappeared, and that the lacunary portion of the circulation is in them confined to the head. So far as I have yet examined the genera Loligo and Sepia, it appears that the abdominal portion of the great blood sinus is really wanting, as is asserted by this distinguished French anatomist; but in Ommastrephes todarus this is not the case, the middle portion of the sinus still existing in a modified form. The posterior division has certainly disappeared, and with it the two posterior venous trunks which pass from it to the venæ cavæ. The anterior venous trunk is, however, present, and passes forward by the side of the aorta, and with it ascends until it reaches the dorsal surface of the liver, exactly as it does in the Octopodidæ. The two vessels then run along for a short distance by the side of the œsophagus, when the venous trunk suddenly expands, and, enclosing that tube within it, forms for it a wide sheath. In this state, with the aorta imbedded in the wall of the sheath, the œsophagus and vein reach the salivary glands, when the vein or sheath again expands, and forms a pouch for the reception of these organs. The œsophageal sinus thus formed, and carrying within it the œsophagus, salivary ducts, and buccal branches of the aorta, passes through the nervous collar, and becomes continuous, in the usual way, with the anterior or buccal division of the sinus.
Here, then, we have a modified visceral sinus; and so modified, that its true nature is patent enough. In the first place, it cannot be doubted that this is the homologue of the so-called visceral chamber in the Octopodidæ; or, rather, of what has been termed the œsophageal or median division of it. It contains the same organs, is situated in the same position, and communicates in like manner with the anterior or buccal division of the sinus and with the left vena cava. I have just said it contains the same organs. The aorta, however, might be supposed to be an exception to this; but as it lies apparently in the wall of the sinus, and not merely attached to it, it may be considered to rest virtually within the sinus,—the wall of the sinus itself, as in the Octopodidæ, being reflected over it.
This modified visceral sinus lies packed in a rather loose areolar tissue, but can be easily isolated; so that no doubt can exist as to the fact, that its wall is really an expansion of that of the venous trunk, which communicates with the vena cava. And thus we arrive at the conclusion that the so-called visceral chamber in the Octopodidæ is a veritable venous sinus, with its own proper wall.
As this so-called abdominal or visceral cavity is the only hiatus in the vascular system, pointed out by Milne Edwards, we might perhaps assume, since we see that this is really a venous expansion, that in these animals we have a completely closed blood system, with proper walls throughout. There is one point, however, which appears still to require elucidation before we can finally adopt this conclusion. The existence of capillaries has not yet perhaps been sufficiently demonstrated. Milne Edwards apparently believes in their presence; but he has not described them, neither are his figures satisfactory on this point. And I am sorry that I cannot myself speak to the fact with sufficient confidence; but as I have succeeded in injecting a minute network of vessels on the stomach in one instance, and that not under the most favourable circumstances, I cannot doubt that the peripheral portion of the vascular system is as complete as the central, and that I shall be able to demonstrate this so soon as I shall obtain suitable and fresh specimens. Neither must we forget that Kölliker (Entwickelungsgeschichte der Cephalopoden), states that he has observed capillary vessels in the embryo of Sepia, and that H. Müller describes them. We may therefore, I think, fairly assume, for the present, that the vascular system is throughout supplied with proper walls. And here the question naturally arises, How then does the chyle enter into the circulation?
From whatever point of view we look at this important question, we find it beset with difficulties. Supposing, for instance, that we adopt the opinion of Milne Edwards, that the great dorsal blood sinus is nothing more than a visceral chamber, more or less developed, forming an extensive hiatus in the continuity of the vascular system, it is not easy to see how the chyle could find its way into this reservoir, even were it devoid of walls. In those mollusks which have the intestine floating in the visceral chamber, the chyle may be supposed to exude through the walls of that tube, and thus at once pass into the circulation. But in the Cephalopoda the intestine is not so situated. On the contrary, it is placed on the ventral, or opposite side of the body, having the liver above it. It is not, however, in contact with that viscus, but is separated from it by a stout muscular membrane, which entirely cuts the intestine off from all communication with every portion of the so-called visceral chamber. In fact, in most of the Loliginidæ, the greater portion of the intestine is placed, along with the great cephalic vein and duct of the ink-bag, in a confined space, bounded above, by this membrane, below, by the external wall of the abdomen, and behind, by that of the renal chamber: in front, the space is closed by the coalescence of the said membrane and the abdominal wall. And here the intestine lies closely packed in juxta-position with the above-mentioned organs; the whole being bound together and firmly attached to the surrounding walls by areolar tissue. In the Octopodidæ, the intestine is also to a great extent similarly situated; but the convoluted portion is thrust further back between the wall of the renal chamber and that of the right side of the abdomen. How, then, the chyle is to find its way from the intestine to the so-called visceral chamber it is impossible to say. Milne Edwards does not explain how this is effected: on the contrary, his injections prove that the visceral chamber is bounded by a wall, and is entirely cut off from the space in which the intestine is placed.
The difficulty is not much lessened by assuming the absence of capillaries; for nearly all the viscera, whose veins might be supposed to take up the chyle mingled with the extravasated blood, are confined in chambers which are equally cut off from the space in which the intestine is placed. The venous radicles of the abdominal walls in the vicinity of the intestine might possibly absorb the chyle; but the anatomy of the parts shows nothing to warrant such an opinion.
After weighing this point with much care, I am forced to the conclusion, which must have been generally adopted when the macular system in the Mollusca was thought to be complete, that the absorption is effected through the instrumentality of the intestinal veins themselves, which are amply provided, and are every way suitable, for such a purpose. There are usually two or more such veins; and in the Loliginidæ they are placed symmetrically, on each side of the alimentary tube, and have the portions which lie within the renal chamber covered with glandular appendages, similar to those that garnish the venæ cavæ. They always open into the venæ cavæ, or into the great cephalic vein, close to the point where the latter gives origin to the former, and are richly provided with twigs.
Now, it would seem that it must be through the agency of the capillaries of these vessels that the chyle, or nutritive fluid, finds its way into the circulation. These capillaries probably penetrate to the folds of the mucous membrane that lines the intestinal tube, and there assuming the office of lacteals, in addition to that of veins, take up, by a species of endosmosis, the nutritive products of digestion. Or, it may be that, spreading out over the surface of this portion of the alimentary tube, they there meet with and absorb the exuded chylous fluid.
There is nothing that should startle us in the idea that these veins act in a double capacity, for everywhere throughout the animal kingdom we observe one and the same organ performing several functions, until the division of labour in organic life is fully consummated. And in the embryo of the higher animals the absorption of the nutritive matters is actually effected by the sole agency of the vascular system. Thus, in the embryo of the fowl, the yolk is absorbed by the blood-vessels of the germinal membrane; and the nourishment of the mammalian embryo is accomplished by the aid of the vascular tufts of the umbilical vessels, which likewise absorb the required oxygen from the blood of the parent. So that, in the latter case, these blood-vessels do not only act as lacteals, but also perform the function of lungs.
The chyle, then, in the Dibranchiate Cephalopoda appears to be absorbed in this way by the intestinal veins, and to be poured by them, mixed with the blood coming from the intestinal tube, into the venæ cavæ, and there commingled with the blood returning from all parts of the system, to be subjected, on its way through the branchial hearts to the aerating organs, to the action of the renal follicles.
These hearts are of a very peculiar appearance; so much so that their cardiac nature has been denied. Their walls are exceedingly thick, soft and spongy, and are composed, for the most part, of nucleated granular cells. On this account they are considered by some anatomists to be glandular organs,[1] which undoubtedly they are; but it is erroneous to assert that they "contain no trace of muscular fibres." Such fibres assuredly exist, and are most plentiful, lining the inner surface of the cavity, where they form numerous circular meshes of various sizes, bordering the orifices of the channels, that permeate the substance of the organ in all directions. Fibres, also, pass in every direction through the glandular mass of the walls. There can, therefore, be no question as to their being blood-propelling organs, though they are at the same time glandular.
Attached to these curious compound organs are the so-called "fleshy appendages" before alluded to, the true nature of which is still an enigma. They are usually of a rounded form, smooth externally, with the interior cavernous, wrinkled, and irregularly laminated. They are attached to the heart by a short, constricted peduncle and, on the opposite surface, there is an irregularly-formed opening, leading into the interior. The walls of the organ are composed almost entirely of a soft, tender parenchyma, formed, for the most part, of vascular ramifications, the trunks of which, three or four in number, communicate with the interior of the branchial heart, through the peduncle. The walls of these trunks and of the peduncle are composed of stout, tough membrane. The cavity of the appendage does not communicate with that of the heart, but opens, as we have seen, externally, or into the chamber within which the organ is placed, so that the fluid surrounding it will bathe its inner as well as its outer surface.
On examining microscopically, the membrane lining the inner surface, it is seen to be covered with minute, obtuse, cylindrical papillæ, filled with very small granular cells.
Difficult as it has been to determine the anatomy of this organ, it is still more so to assign to it its proper function, though it is evidently of much importance in the economy of these animals. We have seen, in the Loliginidæ, that these appendages lie within the great genital chamber, and are bathed by the fluid therein contained. And where, as in the Octopodidæ, this chamber is modified, there is a special apparatus provided, by means of which the appendages are still kept in contact with the fluid coming from that chamber. They therefore appear to have some relation to this fluid, the nature of which it becomes of importance to examine.
But first as to the genital chamber itself, and the others associated with it. In the Octopodidæ, as we have seen, there are five of these chambers, and only two in the Loliginidæ. These two, however, are homologically equivalent to the five in the former; which are made up by the renal chamber being divided by a septum, and by the two small additional, lateral chambers containing the cardiac appendages, the lateral chambers themselves being nothing more than developments of the passages connecting the genital with the renal chamber.
As the glandular appendages of the venæ cavæ are now generally acknowledged to be of a renal nature, the office of the chamber containing them is, apparently, to receive the urine as it la secreted, and then to expel it through the nipple-shaped orifices situated in the branchial chamber. And the genital, which we have seen communicates with the renal chamber, may be looked upon as an extension of the latter; the same membrane undoubtedly forming the walls of both chambers. In the renal chamber proper this membrane is in part specialized, forming the glandular appendages attached to the venæ cavæ, the blood channels themselves only supplying the vessels that permeate these organs. The effete, nitrogenous and more solid matters of the urine are probably eliminated by these glandular appendages, which take upon themselves the function of the urinary tubules of the kidneys of the higher animals; while the other great chamber, the genital, receives the fluid, perhaps little more than water, that may be supposed to flow from the arterial capillaries of the various organs placed within it. Assuming this to be the case, then this chamber will be related functionally to these capillaries as the capsule of the malphigian tuft is to the capillaries of the tuft itself. The fact appears to be, that the kidney in these, as in most other mollusks, is diffused, or not fully specialized; but nevertheless here, as in the higher animals, the more solid products of the urinary secretion are abstracted by the agency of secreting cells, and the fluids principally by the action of mere capillary blood-vessels.
This, then, is apparently the primary function of these so-called water chambers; but lymph may also be supposed to escape into them during the act of nutrition, and mingle with their fluid contents. This, however, is perhaps more strictly the case with regard to the genital chamber, in which the fluid is probably little else than lymph and pure water; the valvular nature of the orifices connecting this chamber with that containing the glandular appendages preventing the fluids of the latter passing into the former. The deleterious urinary matters are consequently always confined to the renal chamber proper.
Now we have seen that the cardiac appendages are always bathed by this fluid, both externally and internally, however the parts may be modified; that their lining membrane is raised into folds and wrinkles, which are clothed with minute papilla?, thus giving great increase of surface; that the papillæ are filled with granular cells, and are in connexion with a highly vascular parenchyma, and that the trunks of the vessels permeating this parenchyma, open into the branchial hearts. It is therefore evident, from the structure of these enigmatical organs, that they are well calculated for the selection and absorption of fluid matters. I would suggest, then, that we see in these cardiac appendages an apparatus for the return to the system of the extravasated lymph that may have escaped into the genital chamber, and that consequently we have here a rudimentary form of the lymphatic system.
This suggestion is to some extent corroborated by the nature of the branchial hearts, into the midst of the glandular walls of which the lymph is apparently thrown, and there probably undergoes some assimilating influence, on its passage into the circulation, like that which is supposed to be exercised by the spleen, and the other glandular appendages in connexion with the lymphatic system of the higher animals.
It would thus appear that these so-called water chambers form a diffused kidney, having, probably in connexion with it, a rudimentary lymphatic system. It is, however, generally believed that they receive water into their cavities from the exterior; but it is not easy to conceive for what purpose the raw element should be thus admitted to bathe the surfaces of the various delicate organs that lie within these cavities. There is nothing to give colour to such an opinion, except the fact that the renal chamber opens externally; and yet it would have been rather extraordinary if no such orifice had existed to admit of the escape of the urine. And, moreover, it is evident that this opening, which is, so far as my experience extends, always more or less nipple-formed, is ill calculated for the ingress of fluid, while, on the contrary, it is perfectly adapted for its egress. The same is the case with regard to the passages of communication between the renal chamber and the other portions of this so-called water system. This is most strikingly so in the Loliginidæ, in which it would seem impossible for the fluid in the renal, to pass in a backward direction into the genital chamber; though the passages are most admirably formed to allow the flow of the fluid in the opposite direction,—the tubes connecting the two chambers opening into the renal chamber, much in the same manner as the ureters do into the bladder of the higher animals.
Neither have I yet been able to satisfy myself of the existence of any water canals, or system of water chambers, opening externally in the neighbourhood of the head or tentacles. Some writers appear to have taken the olfactory openings for orifices leading into such aquiferous passages or chambers, and probably some of the other openings described, are nothing more than mucous pores. But this branch of the subject requires further investigation.
Before concluding, one or two points of detail may be mentioned in connexion with the vascular system. With regard to the heart, I can find nothing deserving the name of pericardium. The renal chamber has been so designated; but, as we have seen that the heart is never placed within it, this is evidently a misnomer. The heart, in some of the Loliginidæ, lies within the genital chamber, but is not enclosed in a special receptacle. The membrane, forming the wall of the chamber, is apparently reflected over it, though it is so completely incorporated with the surface of the organ as not to be demonstrable. In the Octopodidæ the heart lies in the cellular tissue, between the renal and genital chambers, and is more or less enveloped by the wall of the former : but here, as in the other group, there is no pericardial sac.
The heart itself is strong and muscular, and the fibres are of the striated kind. Those of the branchial hearts are also apparently striated, but the striæ are less distinct, owing perhaps to the state of preservation of the specimen examined. Striated fibre has likewise been observed in these parts by H. Midler.
The ascending aorta, on reaching the cranium, is divided into two nearly equal portions, each of which has, near its origin, a conspicuous bulbous enlargement. Numerous branches radiate from these bulbs, and are distributed to the brain, to the eyes, to the œsophagus, to the salivary glands, to the buccal organ, and to the arms. The branches that go to the buccal organ pass through the nervous collar; and that which supplies the arms goes so far along with them, and then penetrating through the pedal ganglion, passes to its outer surface, and so advances to its destination, giving off, as it goes, branches to the muscular wall of the buccal channel.
The arterial branches supplying the fins in the Loliginidæ, exhibit enlargements similar to those of the aortic branches, and the function in both cases is probably the same, though it is not very clear what it is. As they are muscular, however, they are probably for the purpose of regulating the flow of the blood to the respective parts, retarding it or pressing it onward, as occasion may require.
The most interesting point that I have observed in the nervous system is, that the surface of the brain of Octopus vulgaris displays distinct inequalities, having a considerable resemblance to the rudimentary cerebral convolutions of some of the lower Vertebrata. I have also, for the second time, observed that the brachial nerves originate in two centres, or rather, that in those species which have the pedal ganglions divided into two portions, these nerves have double roots which can readily be separated for a considerable distance from their origin.
It may also be stated, that, on a due analysis of the parts, the commissures and the ganglions, composing the Cephalopodous brain, can be clearly determined, and their homological relations with those of the lower mollusks ascertained. This being so, the difficulties with regard to the general homologies of these highly organised mollusks do in a great measure disappear. And it is satisfactory to know, that the results, thus obtained, agree with those derived from embryological and other data, as determined by Prof. Huxley.
In concluding these few somewhat hasty and imperfect remarks, on the structure and physiology of the Dibranchiate Cephalopoda, it will be well to take a glance at the results at which we have arrived, though in some respects they cannot be considered final.
The results, then, are as follows:—
First.—That the so-called abdominal or visceral chamber, in the Dibranchiate Cephalopoda, is a veritable venous sinus, formed by the expansion of venous trunks, and that it is provided with proper walls.
Second.—That, apparently, capillary vessels exist, uniting the arterial and venous branchlets ; and that the blood system is composed of vessels and sinuses with proper walls, therefore constituting a closed system.
Third.—That the so-called water system, for the ingress of water from the exterior, does not exist; but that the chambers to which this function has been attributed compose a diffused kidney—the glandular appendages in the renal chamber being for the purpose of eliminating the peculiarly urinary matters, while the fluids pass off through the agency of the capillaries of the various organs that lie in the several chambers.
Fourth.—That a rudimentary absorbent system exists in these animals, the intestinal veins assuming, in addition to their own, the function of lacteals, and the so-called fleshy appendages of the branchial hearts acting, probably, in the capacity of a general lymphatic system.
Fifth.—That there is no pericardium properly so called.
Sixth.—That the muscular fibre of the systemic heart is of the striated variety, as is also apparently that of the branchial hearts.
Seventh.—That the cephalic arteries, and those supplying the fins, are provided with bulbous, muscular enlargements, probably for the purpose of regulating the flow of the blood.
Eighth.—That the surface of the brain of Octopus vulgaris exhibits inequalities resembling rudimentary convolutions, and that the pedal nerves arise by double roots; both conditions approximating to the higher standard of the Vertebrata.
Ninth.—That the results of analysis of the nervous system corroborate the deductions derived from embryology as to the homological import of the parts.
- ↑ Anatomy of the Invertebrata, by C. Th. v. Siebold, translated by W. J. Burnett, p. 292.