2QO WALTER E. CARREY. 



often observed that fertilization is possibl'e even before the 

 nuclear membrane begins to fade. After both polar bodies were 

 formed I found that fertilization by any means caused the forma- 

 tion of the membrane between them and the egg surface, from 

 which they were lifted and pushed away as the membrane moved 

 outward. They are seen to lie in the saucer-like depression in 

 the outer surface of the membrane, which results from the 

 resistance offered by the egg-jelly to the pressure developed in the 

 perivitelline space. After staining with dilute methylene blue, 

 examination removes all doubt that the polar bodies are entirely 

 outside the membrane. 



By so timing the fertilization that only the first polar body has 

 been formed, it will be pushed away from the egg outside the 

 fertilization membrane while the second polar body, being formed 

 much later, remains at the surface of the egg, and therefore inside 

 the perivitelline space. Similarly by fertilizing before matura- 

 tion the fertilization membrane will have been formed and will 

 have left the surface of the egg before the polar bodies are ex- 

 truded. These remain at the surface of the egg and therefore 

 within the perivitelline space. By manipulation they may be 

 shaken free from the surface of the egg and moved about freely. 



IV. Kite 1 has stated that the "so-called fertilization membrane 

 of the egg of Arbacia consists of three parts, viz., the inner layer 

 of the egg jelly which has undergone a change in refraction index, 

 the swollen vitelline membrane, and the thin highly refractive 

 surface layer of the cytoplasm. This hyaline layer is still very 

 adherent to the vitelline membrane." Kite thus conceives the 

 vitelline membrane to remain attached to the egg, to become 

 swollen and edematous and to fill completely the entire space 

 between the egg and the jelly which in turn is altered in refrac- 

 tive power to appear like a separate membrane. That the egg 

 jelly is non-essential has been shown. The other features of 

 Kite's conception can likewise be demonstrated to be erroneous 

 both for Arbacia and Asterias. In these forms what appears to 

 be the fertilization membrane is far more than the outer refractive 

 part of an invisible thick layer of "gel" formed by a swelling of 

 the vitelline membrane. It is a true, thin membrane formed 



1 Kite, G. L., Science, 1912, N.S.. XXXVI., 562. 



