U2 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



penis. In Peronia, the vas deferens and the oviduct open 

 together by the genital aperture, and, as in some Branchio- 

 gasteropods, a groove, along which the seminal fluid is con- 



FiG. 123. — Dinsrram exhibiting the disposition of the intestine, nervous system, etc., 

 in a common Snail (Hdix). — a, mouth; ft, tooth ; c, odontophore ; d, gullet j e, its 

 dilatation into a sort of crop;/, stomach; g, coiled termination of the visceral 

 mass ; the latter is also close to the commencement of the intestine, which will be 

 Been to lie on the neural side of the oesophagus ; A, rectum ; t, anus ; A*, renal sac ; 

 ;, heart; m, lung, or modified pallial chamber; n, its external aperture; o, thick 

 edge of the mantle united with the sides of the body; J9. foot; r, s, cerebral, pedal, 

 and parie to-splanchnic ganglia aggregated round the gullet. 



duoted, leads to the outer opening of the eversible penis (Fig. 

 123, I., II.). 



In connection with the female genital aperture, there is 

 always a spermatheca., or sac (which is sessile in the Slugs, 

 but in the Snails is placed at the extremity of a long duct), 

 for the reception of the semen of the other individual when 

 copulatioti takes place. 



The Ilelicidm alone possess, in addition, the so-called sac 

 of the dart^ a short muscular bag, in which pointed ciiitinous 

 or calcified bodies — the splcula amorls — are formed ; and 

 certain glandular coeca, generally arranged in two digitate 

 bundles, termed mucous glands, which give rise to a milky 

 secretion. Sometimes prostatic glands are developed on the 



