THE ECTOPLASM 



changes largely concern the ectoplasm, as the appended 

 figures (9) show. Though I have sought to obtain these 

 stages in other species of sea-urchins, I have so far failed. 

 In mature echinoderm eggs the ectoplasm, though difficult 

 to observe, can be made out in the living egg as a homo- 

 geneous extremely narrow rim beneath the vitelline mem- 

 brane. In fixed preparations it is only very faintly marked 

 oflF from the endoplasm. After fertilization the ectoplasm 

 stands out clearly because of the now present hyaline 



Fig. 9. — Development of the ectoplasm in the egg of Toxopneustes variegatus 



(after Selenka). 



95 



