YII 



MOLLUSGA—THE PALLIAL COMPLEX 



73 



reaching so far forward that the anus is found near the right edge of the mantle cleft. 

 There is only one nephridial aperture to the left of the base of the ctenidium, far up in 

 the mantle cavity. The inner surface of the mantle, between the rectum on the right 



Fio. 71.— Pyrula tuba, male, taken out of the shell (after Souleyet). The mantle is cut open 

 along its base and right side, and laid back to the left ; the position of the pallial organs is thus 

 reversed. 1, Proboscis; 2, snout ; 8, foot ; 4, penis ; 6, seminal duct, which is continued at 16; 

 6, floor of the pallial cavity = nuchal integument; 7, columellar muscle; 8, intestine; 9, heart ^in 

 tiic opened pericardium ; 10, digestive gland (liver) ; 11, testes ; 12 and 13, renal organs ; 14, renal, 

 aperture ; 16, seminal duct ; 10, rectum ; 17, hypobranchial gland ; IS, anus ; 19, ctenidium (gill) ; 

 20, mantle ; 21, osphradium ; 22, respiratory siphon. 



and the gill on the left, is glandular, and represents the slightly differentiated hypo- 

 branchial gland. The genital aperture lies close to the anus. 



Docoglossa.— In the Patelliihi: (Figs. 69, 70) a short conical portion of the 



