THE LIFE-HISTORY OP NUCDLA DELPHINODONTA. 351 



the loop that occurs in adult Yoldia limatula (Text-fig. L). 

 The dorsal bend now begins to elongate and project ante- 

 rioi'ly (Text-fig. P). This continues until the loop is ex- 

 tended between the limbs of the loop that was made first 

 (Text-fig. Q). The lower limb of the loop begins to elongate 

 (Text-fig. R), and the adult condition is soon reached (Text- 

 fig. S and fig. 48). 



The heart makes its appearance some time before the loops 



Text-figs. M, N, O, P, Q, R, and S.— Stages in the development of the 

 loops of the intestine in Nucula delphinodonta. 



of the intestine begin to be formed (fig. 41). From the first 

 appeai'ance of its cavity the heart surrounds the intestine. 

 This condition continues for a long time, until the loops of 

 the intestine have been formed, and, in fact, until after the 



