FERTILIZATION REACTION IN ECHINODERM EGGS. 26 1 



is similar to that in other echinoderm eggs. 'The cortex reacts 

 to penetration by pushing out a blister at the site of sperm entry." 

 "From the point of sperm entry a definite gradient of membrane 

 elevation is established, the last point of membrane elevation 

 being at the pole opposite that of successful sperm entry." l 



It therefore appears that in many eggs echinoderms and lam- 

 preys a change in the surface of the egg is initiated by contact 

 of sperm and egg and that this change, which includes membrane 

 separation and elevation, progresses from the point of contact 

 in all directions to the opposite pole of the egg. It is probable 

 that more careful observation would reveal the progressive char- 

 acter of the fertilization reaction in other eggs. 2 The wave-like 

 progression of the reaction irresistibly suggests that electric 

 phenomena are involved ; recently Gray ('22) has made the same 

 suggestion . 



The roughening of the egg at fertilization has also been noted 

 by a few observers. Schticking ('03) and Loeb ('13) record it 

 for echinoderm eggs. The "peristaltic wave" which according 

 to Okkelberg ('14) passes over the lamprey egg in normal fertili- 

 zation or artificial activation is, I think, of the same character. 

 Mr. Leigh Hoadley informs me that a roughening also occurs in 

 the Arbacia egg on fertilization. The cause of the roughening is 

 discussed later. 



Flattening of the egg at the site of sperm entry has also not 

 escaped observation and is regarded by some as a contraction. 

 Hertwig ('78) probably has reference to this flattening when he 

 states that in the starfish egg on fertilization "zieht sich der 

 Dotter von der Eihaut zuriick." Some of Fol's figures ('79) 

 show this flattening and it is also recorded for Toxopneustes by 

 Selenka ('78) and for Petromyzon by Calberla ('78). Schiicking 

 ('03) speaks of a contraction of the egg away from the vitelline 

 membrane and probably has reference to the same phenomenon. 

 The photographs of Ries ('090) of fertilization in Strongylocentro- 

 tus plainly show the flattening at the site of initial membrane 

 elevation and this is also mentioned by him in the text. Elder's 



1 Professor F. R. Lillie informs me that while at Pacific Grove in the winter of 

 1920 both he and his assistant, Mr. J. Nelson Gowanlock, observed the progressive 

 character of the fertilization reaction in Strongylocentrolus. 



2 But not in teleost eggs, according to Reighard '93. 



