MOLLUSCA. 479 



stomach. The focxl of the Aplysia consists of sea-weeds 

 and minute shells. 



The circulating organs are remarkable. On each side 

 the body, in the region of the dorsal plate, there is a large 

 vessel, which receives blood from different parts of the 

 body, and which likewise, by various openings, has a free 

 communication with the cavity of the abdomen. In this 

 respect there is a resemblance to the spongy, glandular 

 bodies of the venae cavae of the Cephalopoda. These two 

 vessels, or vena cava, unite posteriorly, and transmit their 

 contents to the gills. The aerated blood is now conveyed 

 to an auricle, of large dimensions, and uncommonly thin 

 walls, situate beneath and towards the front of the dorsal 

 plate, and emptying its contents through a valve, into the 

 right side of the ventricle. The aorta, which issues from 

 the left and anterior side, divides into two branches, the 

 smallest of which proceeds to the liver on the left. The 

 larger branch is again divided, the smaller branch proceed- 

 ing to the stomach. The largest trunk that remains, be- 

 fore it leaves the pericardium, has two singular bodies at- 

 tached to it, consisting of comparatively large vessels, open- 

 ing from this aortic branch. The use of these glands is 

 unknown. 



The organs of generation likewise exhibit some remark- 

 able peculiarities. The ovarium is situate in the posterior 

 part of the abdomen. The oviduct is tortuous in its course, 

 passes along the surface of the testicle, and, after uniting 

 with a clavate appendage, opens into a common canal. 

 The testicle is firm, apparently homogeneous in its texture, 

 of a yellow colour, with spiral ridges on its surface. The 

 vas deferens arises from a complex, glandular body, and 

 unites with the common canal. This common duct, before 

 it reaches the external orifice, receives the contents of the 

 pedunculated vesicle, and has attached to it a botryoidal, 



