THE ECTOPLASM 



lusia'^ reveals ecto-endoplasmic differentiation. The egg of 

 Amphioxus^ likewise has an outer sheath of cytoplasm 

 marked off from the inner (Fig, 15). The ectoplasm 

 of the latter e.gg as pictured by Sobotta recalls that already 

 above described for the e^g of Nereis or of the sea-urchin. 

 That all other authors do not note cytoplasmic differ- 

 entiation in the egg of Amphioxus one may attribute 











Fig. 15. — Ecto-endoplasmic differentiation in the egg of Amphioxus (after 



Cerfontaine). 



either to oversight or to the quality of fixation. The 

 separation of the vitelline membrane exemplified by this 

 egg constitutes additional evidence for similarity of its 

 ectoplasmic structure to that of the other eggs named. 

 However, this membrane separation has seldom been 

 observed because of the difficulty of securing the early 

 fertilization-stages for observation. 



^ Meves, igi3. 



- Sobotta, iSg'j; Cerfontaine, igo6. 



99 



