480 THE INVERTEBRATA 



coiled visceral hump which undergoes torsion (which reverses later). 

 The adult shows evidence of streptoneurous ancestry in the presence 



Fig. 356. Mantle cavities of streptoneurous gasteropods. A, Patella, 

 ctenidia absent. B, Fissurella, ctenidia equal; kidneys unequal, like those of 

 Patella. C, Haliotis, right ctenidium smaller; ciliary currents shown by 

 arrows, exhalant shown emerging from the three most recently formed holes 

 in the shell. D, Buccinwn, male, with single set of pallial organs, an. anus; 

 au. auricle; ct. ctenidium; e. eye; exh.c. exhalant current; gon. gonad; inh.c. 

 inhalant current; k.l. left, and k.r. right, kidney; M. mouth; m.s. shell muscle; 

 mu.gl. mucous glands; op.s. opening from mantle cavity through shell; 

 osp. osphradium; op.g.k. opening from gonad into kidney; p. penis; pb. 

 proboscis; rhyn. rhynchocoel; siph. siphon; ten. tentacles; vd. vas deferens; 

 ven. ventricle; int. intestine; ^op. male aperture; rm. rectum. 



of the anus at the right-hand side. In Doris (Fig. 364 B) the anus is 

 median, but the genital aperture is still situated on the right side. 



