CHARLKS B. METZ 



33 



sea water. Similar results are obtained when jellyless eggs are employed in the 

 experiment. However, it must be granted that the last two exi)eriments do 

 not rule out the possibility of an improving action of V'ersene on eggs, for such 

 action might reverse readily upon washing the eggs in sea water (ii8). Such 

 reversal does occur with startish sperm (57). 



Another significant observation from this work is the finding that the quality 

 of fertilization is a function of the sperm concentration both in the presence 

 or absence of a chelating agent. High sperm concentrations produced good 

 fertilization membranes whereas more dilute s[)erm from the same suspension 

 yielded poor membranes. 



In Tyler's material the chelating agents evidently act upon the sperm to 

 improve fertilization, but the mechanism of this action is obscure. Tyler (118, 

 p. 231) interprets his experiments in terms of an impairment of the sperms 

 upon aging "in such a way that, while still capable of fertilization, they cannot 

 elicit a normal response on the part of the egg." This impairment evidently 

 involves the action of metals, but the precise nature of this action is unknown. 

 Nevertheless, the information so far available points up the complexity of the 

 problem of the activation initiating mechanism. 



Graded responses on the part of the egg have long been recognized in par- 

 thenogenetic activation. However, the 'site' of action of parthenogenetic 

 agents is unknown. There is certainly no clear evidence that any of the agents 

 initiate activation through the same route or receptor that operates in normal 

 fertilization (62, 67, 97). Until some clear understanding of the site of action 

 of parthenogenetic agents is available, it would not appear profitable to under- 

 take a comparison of graded responses in the two types of activation. 



The fact that certain graded responses in fertilization, can be ascribed to the 

 condition of the sperm argues strongly against a simple all-or-none, trigger-like 

 activation initiating reaction. 



c) Propagated Responses of Egg at Fertilization. Ujion reaction with the 

 fertilizing spermatozoan, a variety of changes occurs in the egg. Certain of 

 these clearly arise at the site of sperm union and spread in wave-like fashion 

 over the egg surface to meet at the pole opposite the point of sperm attachment. 

 They have been studied most intensively in the sea urchin egg, although other 

 material has been examined recently (17, 21, 73). Most studies on propagated 

 responses of the egg have been concerned with the cortical reaction. However, 

 the effects of fertilization are not confined to the superficial regions of the egg. 

 For example, fertilization induces the egg nucleus to begin or to complete 

 maturation in many forms. Recently Allen and Rowe (7) have observed changes 

 in the endoplasm of stretched sea urchin eggs at fertilization. These changes 

 proceed from the region of sperm attachment and appear to keep pace with 

 the cortical changes. A more thorough study of such endoplasmic responses 

 would be desirable. 



