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
