SECT. 



PHYLUM MOLLUSCA 



763 



reel 



placed, muscular sac, very similar to that of Sepia. On either side 

 there open into it two auricles or efferent branchial vessels, 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 pallial artery (Fig. 691, 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 

 pallial (ant. pall, a.) 

 after giving off arte- 

 ries to the intestine 

 and rectum, and to 

 the branchiae and 

 osphradia, passes to 

 the muscular edge of 

 the mantle, bifurcating 

 anteriorly. Three geni- 

 tal arteries (gen. a. l, f 

 ?, J), supplying the 

 various parts of the 

 reproductive appara- 

 tus, are likewise given 

 off directly from the 

 ventricle. 



A large vena cava 

 (Figs. 690 and 692, 

 ven. c.) occupies a 

 position corresponding 

 closely with that which 

 it occupies in Sepia. 

 It presents the re- 

 markable peculiarity FIG. 691. Nautilus pompilius (male), origin of pallial 



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of being in free com- 

 munication by numer- 

 ous (valvular) aper- 

 tures with the general 

 cavity of the haemocosle. At its aboral end it presents a dilatation 

 from which four afferent branchial veins (Fig. 692, a. I. aff, p. I. aff, 

 p. r. aff, r. ant. aff.) two right and two left proceed to the 

 corresponding ctenidia, at the bases of which veins from the abof al 

 region join them. There are no branchial hearts. 



The renal organs (Fig. 692) are, like the ctenidia and the 

 afferent and efferent vessels, four in number, instead of two as in 

 Sepia. Each renal sac (I. neph. s., r. neph. s., I. post. neph. s., r. post, 

 neph. s.) opens into the mantle-cavity, as already stated, by an orifice 



and genital arteries, ant. pal. a. anterior pallial artery ; 

 eff. br. v. efferent branchial veins ; gen. a. 1, artery to 

 vesicula seminalis (v. sem.) ; gen. a. 2, testicular artery 

 and its branches ; gen. a. 3, artery to pyriform sac ; n. 8. 

 spermatophore-sac ; post. pall. a. posterior pallial artery ; 

 P>jr. pyriform sac ; reel, rectum ; test, testis. (After Willey.) 



