B. CLASS GASTROPODA.t 



"Head distinct, usually furnished with eyes and tentacles; 

 body mostly protected by a spiral or conical univalve shell; 

 lower surface of animal developing a thickened, expanded, 

 creeping disk or foot."* 



FIG. 13. 



Generative apparatus of HELIX. (Semi-diagrammatic, after Lan- 

 kester.) a, ovotestis; b, hermaphrodite duct; c, albuminiparous gland; 

 d, spermatheca; e, uterine portion of hermaphrodite duct; f, f, accessory 

 glands of female duct; h, dart sac; i, vas deferens; k, penis; m, flagel- 

 lum; n, prostate gland. 



The radula, which is a characteristic organ of this class, 

 has been described on pages 41, 42 and 43 of Part I. 



fSince considerable reference is made in the following pages to the genitalia (sexual 

 organs), the annexed cut is introduced to explain the names of the different parts of the 

 system of a hermaphroditic gastropod mollusk (Fig. 13) . 



*Tryon, S. & S. Conch., Vol. II, p. 99. 



