THK DKVELOPMKNT OF PALUDINA. 



139 



subject of the asymmetrical shape of the body will be alluded to 

 further on (p. 143). 



S s ™h 

 ma jnr 



Fig. 59. — A-C, embryos of Paludina oivipara of different ages (after v. Erlanger). 

 <*, anus ; an, eye \f, foot ; h, heart ; /, liver ; lp, left pericardial sac ; m, mouth : ma, 

 enteron ; mj\ mantle-fold ; nth, mantle-cavity ; mr, edge of the mantle ; na, efferent 

 renal duct ; ot, otocyst ; p, pericardium ; s, shell ; .<•■/', shell-groove ; sy, edge of shell ; 

 I, tentacle ; wn, primitive kidney ; c, velum, 



It has already been mentioned that the anal aperture lies in the 

 mantle-cavity. This latter has deepened during the processes just 



