IX 



MOLLUSCA 



347 



Ut 



ur 



m.c 



e.o 



FIG. 277. -Diagrammatic transverse sections of young specimens of Dreissensia 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 limb into the ureter. C, the outer limb becomes bent inwards toward 

 the middle line. D, the two inner limbs the rudiments of the ureters fuse in the middle line. E, the 

 internal and external openings are formed. e.o, external opening of the kidney ; int, intestine ; i.o, in- 

 ternal opening of the kidney ; l.k, left kidney ; m.c, mantle-cavity ; r.k, right kidney ; r.p, reno-peri- 

 cardial canal ; ur, xireter. 



