VASCULAR SYSTEM. 39 



communication with the body cavity, and ramifies through the 

 pedal mass (pi. 3, fig. 18). It has been observed in Murex, 

 Dolium, Triton, Strombus, Buccinum, and many other genera. 

 In Nerita canrena Delle Chiaje saw the water spirted from a 

 number of holes in the foot. 



The statement of the existence of the remarkable communica- 

 tion of the abdominal sinus with the surrounding water was 

 received with little faith, and the subject attracted as little atten- 

 tion, though immediately after Delle Chiaje's discovery, R. E. 

 Von Bar had fully demonstrated its existence in the lamelli- 

 branchs, until finally Agassiz made known his weighty confirma- 

 tory and thorough observations. In Pyrula carica and P. 

 canaliculata, Agassiz observed a large pore in the pedal disc, 

 which is so large that it will admit a goose-quill, and which is 

 divided into many branches throughout the foot, which open, by 

 means of numerous finer branches, into the abdominal cavity. 

 Agassiz injected carmine or indigo solution through this pedal 

 pore, and it filled not only the pedal canal system, but also the 

 body cavit} r and, finally, the whole vascular system. Quite 

 similar relations were found by him to exist in Mactra. The 

 water actually mixing with the blood in this manner, Agassiz 

 also showed thereby that the blood was exhaled from the body 

 cavity, salt crystals also being observed, which were derived 

 from the sea-water which had been taken up. It has been known 

 for a long time that univalves when removed from the water 

 allow considerable water to escape from them, which runs out of 

 the foot. Agassiz found numerous blood corpuscles in this 

 water, and there can, therefore, no longer be any doubt that 

 water passes through the pedal pore into the abdominal or body 

 cavity, where it is mixed with the blood.* 



* On the other hand, the researches of Mr. Wedl have led him to an- 

 nounce the existence in the mollnsca of a completely closed vascular 

 system, with capillary networks in the greater part of the organs. The 

 type of distribution of these is extremely variable, and intimately connected 

 with the structure. It is thus that in the Murices the skin of the trunk 

 and of the back is formed of several superposed layers of muscular fibres, 

 crossed in different directions, and that several networks of blood vessels 

 are likewise superposed in these parts. The vascular networks are super- 

 posed in the same manner in the foot of these Ctenobranchs. In no part 

 of the skin is there any communication between the veins and the ex- 

 terior ; nor do the veins appear to communicate with the aquiferous ves- 

 sels. M. Wedl, however, has not been able to determine whether these 



