FERTILIZATION REACTION IN ECHINODERM EGGS. 269 



plasm and acquires a definite internal boundary which it had 

 hitherto lacked ; l and (b) a new surface is formed on the egg 

 cytoplasm, the so-called hyaline layer, which prevents the egg 

 contents from expanding with the membrane and which replaces 

 physiologically the vitelline membrane. The separation of the 

 vitelline membrane from the egg cytoplasm at fertilization thus 

 appears to me to be a process quite independent of the subsequent 

 elevation of the membrane. The hyaline layer which replaces 

 the vitelline membrane requires some time for its complete 

 development and is according to Chambers ('216) "firm and 

 gelatinous." 



An increased viscosity accompanying the fertilization reaction 

 has not been hitherto recorded. Several observers have, however, 

 noted such an increase following after fertilization, recently 

 Heilbrunn ('15, '200, '21), Chambers ('176, '19), and Seifriz 

 ('20). According to these investigators the increased viscosity 

 is associated with some phase of the mitotic figure. According 

 to Chambers ('176) the gelation after fertilization is at first 

 limited to the small sperm-aster and later spreads throughout 

 the egg. While fully accepting the conclusion of these authors 

 that asters and spindles are gelation figures I do not think that 

 the initial gelation which constitutes part of the fertilization 

 reaction is due to the sperm aster. The latter is at first localized 

 around the sperm head while the gelation which I am considering 

 appears to be general throughout the whole cortical region of the 



egg- 



Since the viscosity changes at fertilization precede the elevation 

 of the membrane it may be emphasized that the latter is a secon- 

 dary rather than a primary phenomenon in the fertilization 

 reaction. It seems certain that changes have taken place in the 

 egg before the membrane elevates. This has recently also been 

 emphasized by Just ('19): "In the Echinarachnius egg, normal 

 development has already been initiated by the sperm when the 

 membrane begins to form." It appears that the elevation of the 

 membrane is not due directly to sperm penetration but is the 

 result of changes in the egg. 



6. Artificial Membrane Elevation and Cytolysis. It is well 



1 Fol ('79) in particular emphasizes that the vitelline membrane (couche envel- 

 oppante) lacks a definite internal boundary and that it acquires one at fertilization. 



