IX 



MOLLUSCA 



347 



inl 



Ik 



B 



m.c 



e.o 



e.o 



FIG. '111. Diagrammatic transverse sections of young specimens of Ureis-iensii* polymorpha 

 in order to illustrate the development of the kidney. (After Meisenheimer.) 



A, the kidney a round sac. B, the kidney assumes a U -shape the outer limb develops into the 

 glandular portion, the inner Hint) into the ureter. C, the outer liinli beronifs lient inwards toward 

 the middle line. D, the two inner limbs the rudiments i>r the ureters fuse in the middle line. E, the 

 internal and external openings are formed. f.<>, external opening of the kidney ; hit, intestine ; i.n, in- 

 ternal opening of the kidney ; I.I.-, left kidney ; m.c, mantle-cavity ; r.k, ri.uht kidney ; r.p, reno-peri- 

 cardial canal; ur, ureter. 



