184 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



From the dorsal side of the innominates, near the origins of the inferior mandibular arteries, 

 arise arterioles which pass into the cerebral ganglia. From the posterior side of the innominates 

 other small vessels pass into the posterior portion of the hood. 



Finally, each innominate divides, one branch passing backward into the shell muscles and 

 forming the anterior columellar artery, the other branch passing forward and downward along 

 the bases of the tentacles, forming the pedal artery. Near the base of the pedal artery two 

 arterioles pass outward to the eye. Between these a large branch arises from the pedal artery 

 which passes to the funnel, the infundibular artery. The remainder of the pedal artery, which 

 gives off branches to the individual tentacles, Willey has very conveniently named the tentacular 

 artery. The first of the branches of the tentacular artery passes into the inferior labial lobe in 

 the female, and into Van deb Hoevkn's organ in the male. 



The origin of the genital and gonaducal arteries and the artery of the pyriform sac has 

 already been mentioned. 



The genital artery passes from the heart directly back upon the gonad, in which it breaks 

 up into capillary branches. 



The gonaducal artery passes to the right from the heart and is distributed to the walls of 

 the functional genital duct. 



The artery of the pyriform sac, or the non-functional genital duct, passes to the left from 

 the heart and extends along this organ. 



Willey shows that both the gonaducal artery and the artery of the pyriform sac give off a 

 branch which passes into the perigonadial membrane, and he says: "This apparently trifling fact, 

 combined with the subsymmetrical relations of the gonaduct and the pear-shaped gland, may 

 indicate that the latter is the metamorphosed genital duct of the left side, and not, as I believe 

 has been suggested, the morphological equivalent of an entire left genital apparatus." 



Almost immediately after its origin from the anterior side of the heart, the lesser aorta 

 divides into two branches. 1 One, the pallia! artery, runs straight forward in the median line of 

 the mantle and is distributed to the intestine, rectum, and mantle. The other, the common 

 septal artery, runs almost straight backward and is distributed entirely to the septal portion of 

 the body wall and the siphuncle. 



The pallial artery is inclosed by the pallio-visceral ligament, A few millimeters anterior to 

 the heart it gives off a slender branch (the intestinal artery), which runs hack in the membrane 

 uniting the two portions of the second loop of the intestine. Small arterioles pass from either 

 side into the intestinal tissues. 



In front of the intestinal artery several small rectal arteries arise directly from the pallial 

 artery and pass to the walls of the rectum. 



At the point where the two walls of the mantle fold unite and the mantle becomes thin, a 

 pair of vessels arise from the pallial artery and pass outward to the right and the left in the sub- 

 stance of the mantle. These arteries, discovered by Willey. were called by him the branchio- 

 osphradial arteries, "since among their minor ramifications they send up branches to the tips of 

 the branchiae, supplying the integument of the latter, and also a small branch into each of the 

 osphradia." In the female the nidamental glands are supplied by branches of the branchio- 

 osphradial arteries. I retain the name " branchio-osphradial " for these arteries because, although 

 the osphradia] character of the papillae referred to is not yet well proven, there is still a consider- 

 able probability of it, and it does not seem worth while to burden the literature of the subject 

 with a new name which might in time prove more correct, but for the present would be no more 

 intelligible or convenient. 



The pallial artery now passes forward nearly to the mantle edge. It here divides into a right 

 and a left branch (the marginal pallial arteries), which run parallel to the edge of the mantle till 

 they unite dorsally with the pallio-nuchal branches of the dorsal aorta. In this way a remarkable 

 arterial circuit is formed, to which Willey has given the name "circulus pallialis." 



'The arteries described after this are represented in text-rig. 11. 



