476 OEiaiNAL AETICLES, 



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 Octopodidcd, 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 oesophageal, 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 oesophagus, or crop. It contains the gizzard, the 

 spiral stomach or caecum, 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 oesophagus, 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 oesophagus, 

 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 dis- 

 tinctly 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 venae cavse 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 oesophagus, behind and close to 

 the point where the aorta enters the chamber. 



Kow, 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, how- 

 ever, 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 





