PLATHELMINTHES 



179 



Y 



^^pctoderm, and which he believes has arisen, like the envelop- 

 ^^png membrane, as the resalt of an overgrowth coming from 

 one side and surrounding the cell-mass. This, then, would 

 e an epibolic gastrula (Fig. 87 ^ and F). 



The further changes of the embryo consist, in the first 



lace, in the gradual disappearance of the nuclei of the 



toderm cells and transformation of the entire ectoderm into 



Fro. 87.— .4 to fir, embryonic development of Distomum tereticolle (after Schauinf- 

 L and). D, intestine ; Dz, yolk-cells ; Ez, egg-cell ; Ec, ectoderm ; En, entoderm ; Hiii, 

 enveloping membrane ; Kz, cap-cell. 



a thin cuticula-like layer, on the surface of which bristle- 

 like structures make their appearance (Fig. 87 H). A 

 number of the cells of the entoderm have united for the 

 formation of the intestine, which fills about one half of the 

 body (Fig. 87 G). Other entoderm cells are applied to the 

 ectodermal membrane, whereas the remaining cells, lying 

 between these and the intestine, retain the character of 

 embryonic cells. They are germ cells, from which the new 

 generation subsequently arises. Since in the present stage 

 the cells of tlie ectoderm, as well as those which form the 



