THE DEVELOPMENT OF PALUDINA. 



139 



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

 further on (p. 143). 



no. 



'j jnh. 

 ma 



FIG. 59. A-G, embryos of Paludina vivipara of different ages (after v. ERLANGER). 

 a, anus ; au, eye ;/, foot ; h, heart ; I, liver ; Ip, left pericardial sac ; m, mouth ; md, 

 enteron ; mf, mantle-fold ; mh, mantle-cavity ; mr, edge of the mantle ; na, efferent 

 renal duct ; ot, otocyst ; p, pericardium ; s, shell ; sf, shell-groove ; sr, edge of shell; 

 t, tentacle; un } primitive kidney; v, velum, 



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

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



