90 CIRCULATION, AQUIJEROUS SYSTEM. 



Alder records 60 to 80 pulsations in the nudibranchiates. The 

 heart in embryos beats more rapidly than in adults. 



The heart is represented, in the ScajDhopoda hj a pulsatile 

 sanguinary sinus, traversed by the rectum and communicating 

 with a system of lucunse, having no lining walls. 



Lamellihranchiates (vii, 84; viii, 89). The blood is usuallj^ 

 uncolored or slightly bluish, as in the other classes ; in Area 

 pexata^ however, it is red — this specimen being commonly called 

 the "bloody clam." The heart occupies the median line: it has 

 a single ventricle, except in Ai'ca, and two auricles. The ven- 

 tricle is traversed by the rectum, except in Ostrea, Anomia, and 

 Teredo. 



Aquiferous System. Cephalopoda. Dorsal aquiferous pores 

 are found opening upon the head in Argonauta and Tremoctopus : 

 they communicate with large internal cavities. In Ommastrephes 

 and Tremoctopus anal pores, with small cavities, are found on 

 each side of the siphon ; in Onychoteuthis they are placed in 

 advance of it ; in other genera the}^ are wanting. The buccal 

 region in Histioteuthis and Ommastrephes has four aquiferous 

 pores, and there are six of them in Onychoteuthis, in Sepia and 

 in Loligo : the other genera want them. Finally, there are 

 branchial pores situated near the bases of the tentacular arms and 

 between the third and fourth pairs of sessile arms : in Sepia, 

 Sepiola and Rossia they communicate with the great cavities in 

 which are lodged the tentacles when contracted ; in Loligo the 

 smaller cavity only suffices to lodge a portion of the tentacula, 

 and in Histioteuthis, Ommastrephes and Onychoteuthis the 

 cavity is still more restricted, and only occupies a part of the 

 head anterior to the eyes : wanting in other genera. These 

 pores are probably lubricative in function. 



Gastropoda. The aqueous vascular system of the foot and 

 mantle-border forms an important connection between the venous 

 sinus and the external world. It includes one or more pores on 

 the pedal disk of gastropods and lamellibranchiates with direct 

 communication with the body-cavity, and ramifies through the 

 pedal mass (vii, 85). It has been observed as a single pore in 

 Murex, Dolium, Triton, Strombus, Buccinum, and many other 

 genera. In Nerita canrena Delle Chia,je saw the water spirted 

 from a number of holes in the foot. 



The statement of the existence of the remarkable communi- 

 cation of the abdominal sinus with the surrounding water was 

 received with little faith, and the subject attracted as little 

 attention, though iinmediately after Delle Chiaje's discovery, 

 R. E. Yon Bar had fullj^ demonstrated its existence in the 

 lamellibranchs, until finally Agassiz made known his weighty 

 confirmatory and thorough observations. In Pyrula carica and 

 F. canaliculataj Agassiz observed a pore in the pedal disk, which 



