22 CIRCULATION IN CEPHALOPODS. 



branchial veins (vb), the openings of which are furnished with 

 valves, and then penetrates the arteries which arise from this 

 organ. The latter vessels are two or three in number; but one 

 of them is always much larger than the rest, arid one of them 

 also has at its base a swelling or bulb, which is more or less 

 muscular, and analogous to that found at the origin of the aorta 

 in batrachians. The great artery to which we generally give the 

 name of aorta, is carried forward and distributes its branches to 

 a part of the viscera, the head and legs. The other arteries go 

 to the viscera ; and the blood, after having in this way passed 

 through all the organs, returns by the veins, and is emptied by 

 them into a great vena cava, situate near the heart. The bran- 

 chial arteries arise from the inferior extremity of this last vessel, 

 and, in the dibranchial cephalopods, present a very remarkable 

 arrangement ; for, before penetrating the branchiae, each one of 

 them dilates so as to form a great venous sinus (fig. 9, cb), 

 which most authors regard as a branchial heart, but its parietes 

 do not appear to be really muscular. 



5. We see, therefore, that the circulation is here carried on in 

 a manner opposite to that of fishes ; for the heart is found in the 

 track followed by the arterial blood, while in fishes the venous 

 blood passes through this organ ; but in other respects, there is 

 a great resemblance in the general disposition of the circulatory 

 apparatus of these two classes of animals ; for, in both, the 

 blood passes but once through the heart, and the whole of it 

 traverses the respiratory apparatus before returning to the differ- 

 ent organs. 



6. On the vena cava and its principal branches, we remark a 

 multitude of very singular spongy bodies (fig> 9, cs), which, 

 when squeezed, yield a mucosity, and which are attached to the 

 parietes of these vessels ; these appendages are enclosed in two 

 membranous pouches, which perform the functions of a pericar- 

 dium, and, at the same time, communicate by particular openings 

 with the branchial cavity. In this way the water from without 

 laves them, and their interior, which is hollow, communicates by 

 other holes with the interior of the veins, so that the blood must 

 enter them. We know nothing certain in regard to their uses, 

 but it is probable they are the seat of some secretion, and that 

 hey serve as a reservoir to contain the superabundant blood of 

 the veins, when the circulation is interrupted in the vessels, much 

 in the same manner as the spleen seems to do in the superior 

 animals. 



n. How does the circulation in cephalopods differ from that of fishes ? 

 6. What is remarkable about the vena cava ? 



