IX 



MOLLUSCA 



347 



iir 



m.c 



e.o 



ur 



e.o 



Fig. 277. — Diagrammatic transverse sections of young specimens of Dnissensia polymorpha 

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



A, the kidney a round sac. B, the kidney assumes a U-slxape — 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 ; inx, mantle-cavity ; r,h, right kidney ; r.^), reno-peri- 

 cardial canal ; v/r, ureter. • 



