386 A. J. GOLDFARB. 



; 



ter of membrane formation, in aging eggs, are functions largely of 

 the egg and determined by their physiologic condition at liberation 

 and by their subsequent age. Physiologically good eggs form 

 clear membranes rapidly with either fresh or old sperm (the 

 maximum age of such sperm was not ascertained). Physi- 

 ologically poor eggs, form membranes more slowly, closer to the 

 egg surface or do not form membranes at all with either fresh or 

 stale sperm. The change in rate of membrane formation with 

 age, constitutes the third index of the physiologic deterioration 

 of the eggs with age. 



EFFECT OF AGE UPON CLEAVAGE. 

 Synchronous Aging of Germ Cells. 



Aging or physiologic deterioration maybe measured either (i) 

 by a change in size, or (2) a loss of the jelly layer, or (3) a change 

 in rate and character of membrane formation. There is another, 

 more exact and more finely graded index of the changes in the 

 germ cell with age, namely, (4) changes in cleavage. 



Hertwig, '96, and Loeb suggested that with age there was a 

 decreasing cleavage. F. R. Lillie, '14, showed in much greater 

 detail that there was a decrease and indicated the extent of the 

 decrease. 



In Study I., I showed that under constant and optimum condi- 

 tions freshly liberated eggs from different freshly collected fe- 

 males frequently differed widely in the total per cent, of cleavage 

 in a given time, even when fertilized by the same male. In 

 Toxopneustes the different females vary from n to 87 per cent., 

 in Hipponoe from 5 to 81 per cent., in Arbacia from o to 90 

 per cent. Such differences were ascribed to differences in 

 physiologic condition of the eggs of the different females at the 

 time of liberation. 



In preliminary experiments, a given pair of tested sea urchins 

 were used for successive fertilizations. From 100 to 200 of the 

 fertilized eggs were examined at each interval, and the sperm 

 used was freshly prepared from the dry sperm. 



In one group of experiments there was an unmistakeable direct 

 reduction in tJie total cleavage with age. For example, in experi- 

 ment i, the eggs of 3 females were fertilized by one male when 



