EFFECTS OF AGIXG UPON GERM CELLS. 40! 



minutes after fertilization was 76, 65, 44 and 27 per cent, for the 4 

 different ages of the germ cells. The average cleavage 60 minutes 

 after fertilization, for the same ages, was 86, 76, 60 and 39 per 

 cent, and the total cleavage, i. e., 2 hours after fertilization, was 

 91, 91, 71 and 51 per cent, respectively. 



These observations suggest an explanation for the decreasing 

 total cleavage with aging germ cells. For the decreased total 

 may conceivably be due to a retardation of the division process, 

 or an inhibition of this process, or both. 



Records taken three hours after fertilization showed that the 2- 

 hour observation really was the total cleavage; that very little 

 and usually no additional cleavage occurred. Hence the decreased 

 total cleavage with aging germ cells was not an apparent decrease 

 due to retardation, but a real decrease by inhibition of cleavage. 



We are concerned then with two symptoms or independent 

 evidences of changes in the eggs caused by their aging. On the 

 one hand, an increasing number of eggs were prevented from 

 developing and, on the other hand, those that do develop, do so 

 with increasing difficulty (retardation). 



The relation between retardation and reduction in cleavage 

 may be expressed as follows: When germ cells were 130 minutes 

 old, 83 per cent, of the total number of dividing eggs cleaved 

 within 40 minutes after fertilization; when the germ cells were 

 240 minutes old a less number, namely 71 per cent, of the cleav- 

 ing eggs, divided in the same time. When the germ cells were 

 350 and 470 minutes old, 62 and 53 per cent, of the segmented 

 eggs cleaved in 40 minutes. 



In experiment 2, germ cells in poor condition were tested at 8 

 intervals, between J4 hour and 7 hours, and the rate of cleavage 

 noted at each interval. The results are essentially in accord 

 with those of experiment I. The per cent, cleaving in 40 minutes 

 after each fertilization was 36, 2, 3, 3, i, o, o per cent.; for 60 

 minutes after fertilization, the record was 62, 32, 14, 21, 10, o, o; 

 and the total cleavage 2 hours after fertilization was 62, 54, 28, 

 31, n, o, o respectively. 



Experiment 4 is also quite in accord with the previous ones. 



Experiment 3 differs from the above only in the increasing 

 total cleavage for a brief period, followed by decreasing cleavage 



