EFFECTS OF AGING UPON GERM CELLS. 387 



the germ cells were from % to 6 hours old. The per cent, 

 of the total number of eggs that cleaved at each interval was 

 98 per cent, when 17 minutes old, 80 per cent, when 42 minutes 

 old, 70 per cent, when 98 minutes old, 33 per cent, when 161 

 minutes old, 40 per cent, when 214 minutes old, 18 per cent, 

 when 294 minutes old, o per cent, when 360 minutes old. The 

 other 2 females showed corresponding decreases. The average 

 for the 3 females was 94, 62, 54, 28, 31, n and o per cent, re- 

 spectively. See Table 1 1 1. 



In the other group of experiments, there was an initial increased 

 cleavage in the eggs of some or all of the females, followed by a definite 

 and progressive decrease. For example in experiment 6, the eggs 

 of female I and 4 decreased in cleavage with age, as in the first 

 group. But the eggs of females 2 and 3 increased in cleavage for 

 a brief period after the first observation, and then the per cent, de- 

 creased. This appeared to me at the time to be an error in 

 observation, but similar increments occurred in other experi- 

 ments. In experiment 7 the eggs were: fertilized at early and 

 frequent intervals, namely, 7, 20, 43, 59, 89 and 140 minutes. 

 All 5 series of mating showed an early progressive increased cleav- 

 age, followed after I hour, by a decrease. The average for all 5 

 series was 49, 66, 88, 62, 40 and 25 per cent. 



It is probable then that in the other experiments the apparent 

 absence of an initial increased cleavage was due to failure to 

 make sufficiently early and sufficiently frequent intervals, or 

 possibly that the increase in cleavage becomes evident only in 

 eggs in poor physiologic condition. 



In Arbacia only the direct decreased cleavage was observed. 

 Whether an initial increase occurred I cannot say. In the first 

 place insufficient early observations were made, and in the second 

 place, with physiologically good eggs, the maximum or nearly 

 maximum cleavage took place, so that any physiologic change 

 could not be manifested by an increased cleavage. 



Only two experiments are given to illustrate the behavior of 

 aging eggs of Arbacia. In experiment 8, the eggs of five females 

 fertilized by one male, averaged 80 per cent, when 4 hours old, 

 33 per cent, when 23 hours old, o per cent, when 28^2 hours old. 

 (See Table III.) 



