XII 



PHYLUM MOLLUSCA 



785 



there open into it two auricle* or efferent branchial vessels (a. or.), 

 one from each of the four ctenidia. The ventricle gives off a large 

 main aorta (aort.), which passes to the head after giving off 

 arteries to the stomach, the crop, the digestive gland, and the mantle. 

 From the aboral surface of the ventricle arises a smaller artery, the 

 lesser aorta, which immediately bifurcates. One of its branches 

 the posterior pallia! artery (Fig. 682, post. pall, a.) passes to the 

 area of the mantle applied to the septum, bifurcates to supply this 

 area, and gives off a branch to the siphuncle. The other anterior 



gen, A. 3 



FIG. 082. Nautilus pompilius (male), origin of pallial and genital arteries, ant. pul. a. 

 anterior pallial artery ; erf'. ///. ,-. efferent branchial veins ; gen. a. 1, artery to vesicula 

 seminalis (r. sent.) ; gen. a. 2, testicular artery and its branches ; gen. a. 3, artery to pyriform 

 sac ; n. s. sperraatophore-sac ; post. pall. a. posterior pallial artery ; pyr. pyriform sac ; red. 

 rectum ; te*t. testis, (After Willey.) 



pallial (((Jit. pall, a.) after giving off arteries to the intestine 

 and rectum, and to the branchiae and osphradia, passes to the 

 muscular edge of the mantle, bifurcating anteriorly. Three genital 

 arteries ( gen. a. 1 , 2, 3), supplying the various parts of the re- 

 productive apparatus, are likewise given off directly from the 

 ventricle. 



A large vena cava (Figs. 681 and 683, ven. c.) occupies a position 

 corresponding closely with that which it occupies in Sepia. It 

 presents the remarkable peculiarity of being in free communication 

 by numerous (valvular) apertures with the general cavity of the 



