442 



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. 122.— Diagram exhibiting the disposition of the intestine, nervous system, etc., 

 in a common Snail (H-lix).~a, mouth; 6, tooth ; c, odontophore ; <l, gullet ; e, its 

 dilatation into a sort of crop ; /, stomach : q, coiled termination of tne visceral 

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

 seen to lie on the neural side of the ce-ophagus ; h, rectum ; i. anus ; A-, renal sac ; 

 I, heart: m, lung, or modified pallia! chamber ; n. its external aperture ; o, thick 

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

 and parieto-splanchnic ganglia aggregated round the gullet. 



ducted, 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 

 copulation takes place. 



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

 of the dart, a short muscular bag, in which pointed chitinous 

 or calcified bodies — the spicula amoris — are formed ; and 

 certain glandular caeca, generallv arranged in two digitate 

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

 secretion. Sometimes prostatic glands are developed on the 



