443 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 (Hilix). a, mouth ; >, tooth ; c, odontophore ; d, gullet ; 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 inte- a tine. which will be 

 seen to lie on the neural side of the ce.-ophagus ; h, rectum : *, anus ; k, 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; p, foot; 7", 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 Helicidce 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, generally arranged in two digitate 

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

 secretion. Sometimes prostatic glands are developed on the 



