EFFECTS OF AGING UPON GERM CELLS. 13 



DISCUSSION. 



A number of investigators have been struck by the unex- 

 pectedly large variability in the eggs of different females of sea 

 urchins, even when the eggs were liberated at the same time, and 

 kept under apparently identical conditions. A few examples 

 and the explanations offered to account for this diversity may be 

 cited. 



Stockard observed "that a number of eggs when subjected 

 to the same solutions do not all respond in a like manner," and 

 held that such variability was due to "differences in individual 

 resistance and vigor." 



F. R. Lillie also noted "the failure to obtain exactly the same 

 curve . . . ," and believed the result "was due in part to the 

 natural variability of different lots of eggs and sperm." 



Loeb, J., and Wasteneys, H., also believed that this vari- 

 ability was due in large part to differences in the eggs. 



Wasteneys later came to the conclusion that this variability 

 was due to differences in sensitiveness of eggs of different females, 

 and perhaps to temperature. 



R. S. Lillie also held that variability was due to the condition 

 of the eggs. 



F. R. Lillie came closer to an understanding of the matter 

 when he pointed out that "the condition of the eggs whether 

 ripe or immature, fresh or stale, with or without jelly, is more 

 important than concentration of the eggs. The condition of the 

 gonad" he adds, "is the most variable thing in summer sea 

 urchins." 



Loeb ('02) came still closer to the truth, when he stated that 

 "this (variability in maturation of asterias eggs) probably 

 depends on the fact that the eggs of different females are not all 

 in the same condition of ripeness." 



Many other observations might be mentioned in which the 

 authors have either ignored this large variability or, having noted 

 it, ascribed the result to individual resistance, sensitiveness, 

 natural variability and other equally indefinite causes. 



In this connection one must mention Loeb and Chamberlain's 

 work. These authors distinguished between the primary vari- 

 ation in the eggs of a given female, from the secondary variation 



