442 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



penis. In Peronia^ the vas deferens and the oviduct o}3en 

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

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



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

 in a conamon Snail (Hdix).—a, mouth; 6, tooth ; c, odontophore ; d, gullet ; e. its 

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

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

 seen to lie on the neural side of the ce-^ophagus ; h, rectum ; *, anus ; A', renal sac ; 

 I, heart: m, lung, or modifiel pallial chamber; n. its external aperture; o, thick 

 edire of the mantle united with the sides of the body; j). foot; r, s, cerebral, pedal, 

 and parieto-splanchnic ganglia aggregated round the gullet. 



ducted, leads to the outer openino- of the eversible penis (Fig. 

 123, I., II.). 



In connection witli 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 Helicidm alone possess, in addition, the so-called sac 

 of the dart^ a short muscular b;ig, in which pointed chitinons 

 or calcified bodies — the spicula amoHs — 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 



