ir. GASTEROPODA. 



Sir 



grooved dermal fold, the jienh (fig. 370, pe). Occasionally this is 

 separated from the genital jx^re, but is conue('ted with it by a cili- 

 ated groove. 



The terrestrial snails lay their large tongh-shelled eggs in damp 

 earth; in the aquatic forms the eggs are laid in masses, usually 



Fro. 371. — Anatomy of Hdi.v pomaifju tlie roof of the pulmonary sac cut at the h'ft 

 side and turned to the right; tlie pericardium and visceral sac opened ami the 

 viscera separated, (t, anus; c, columellar muscle; J, intestine; cj, alhumen 

 gland ; /, finger-form gland; /?, flagellum; /i/, foot ; y, cerebral ganglion ; /(, heart ; 

 U liver; ?(/, lung ; in, stomach; n, nephridium; n\ its opening; /», penis; /)>■, dart 

 sac: r, receptaciilum seminis; .s, pharynx; xp, salivary gland: u, uterus; c, 

 vagina ; rd, vas deferens ; z, hermaphrodite gonad. 



gelatinous, each egg with a layer of albumen and a firm shell. 

 Occasionally there is a liind of nest, as is tlie case with LtnfJiinu 

 wdiieh carry the mass of eggs, attached to the foot, about with 

 them. A few gastcropods are viviparous. 



In the development the great constancy with wliich the veliger 

 stage (figs. 343, 343) appears is noticeable. ]\[(ist marine larva? 

 swim Ijy their velum (often divided) at the surface before creeping 

 at the bottom. lUit in those cases where the snail leaves the egg 



