218 . TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



anterior aorta, the gastro-oesophageal artery, and the posterior 

 or abdominal aorta. The anterior aorta supplies the mantle, 

 the foot and its appendages, the head and tentacles, the nervous 

 system, the pallial and sub-pallial glands, and the reproductive 

 organs ; the gastro-oesophageal artery sends blood to the 

 alimentary canal ; the abdominal aorta supplies the liver and 

 those portions of the gut and reproductive organs lying within 

 the visceral mass. 



The Anterior Aorta (Fig. 13, ant. ao.) leaves the pericardium 

 on its right antero-ventral face immediately posterior to the 

 parietal and visceral ganglia. At this point a sharp bend 

 forwards occurs, and its first branch is given off to the vesicle 

 of Swammerdam (Fig. 13, sj)th. a.). The aorta then passes 

 to the right of the parietal ganglion and ventral to the nerves 

 issuing from that ganglion. An artery runs dorsalwards to 

 supply the mantle (dors. a.). From the right side of the aorta 

 arise branches to the opaline gland and genifcal organs (gen. a.). 

 The trunk gradually assumes a more median position, and no 

 more branches occur until the nerve ring is reached. The 

 artery does not, however, as in the Snail, pass through the 

 nerve ring, but runs between the pedal and parapedal commis- 

 sures, ventral to the former (i.e., outside the ring) and dorsal 

 to the latter (Figs. 13, 23.). Asymmetrical arteries to foot 

 and body wall are given off, and the now median artery runs 

 forward ventral to the buccal mass, which it supplies with 

 blood. Finally it forks and terminates in the labial tentacles 

 and anterior portion of the foot. 



It must be remembered that in an animal possessing such 

 a high degree of contractility as Aplysia the appearance of the 

 arterial system varies greatly according to the amount of 

 contraction exhibited by the specimen dissected. Thus the 

 aorta at the level of the nerve ring may form a semicircle in a 

 contracted specimen, whereas in an expanded specimen the left 

 pedal artery hooks sharply over the parapedal commissure. 



