EFFECTS OF AGING UPON GERM CELLS. 39! 



as I have shown the results obtained by sperm from different 

 individuals may not be compared without further testing. 

 In this experiment, when the eggs were 225 minutes old, and 

 sperm only 35 minutes old, 32 per cent, cleaved. When the 

 eggs were 250 minutes old and the sperm 60 minutes old, the 

 average cleavage was 45 per cent. Even when the eggs were 

 400 minutes old, and fertilized by freshly liberated sperm, 22 

 per cent, cleaved. Hence it is clear that the decline to the zero 

 mark when both germ cells were 64 minutes old, was due not to 

 the death or incompatibility of the eggs, but of the sperm. 



Even more striking results were obtained in other experi- 

 ments. In experiment 2, for example, cleavage decreased pro- 

 gressively until the germ cells were 420 minutes old, and 6, 

 2 and o per cent, of the eggs cleaved. When the eggs 16 minutes 

 later, i. e., 7^4 hours old, were fertilized by sperm only I hour old, 

 the cleavage was 98, 92 and 60 per cent, or an increase of 80 per 

 cent, over the last reading. When the eggs of these same females 

 were liberated, and immediately fertilized they averaged 80 per 

 cent, hence it is probable that very little real deterioration of the 

 eggs occurred during the first 7 hours after liberation. 



In experiment 3, when the germ cells were both 8 hours old, 

 the average cleavage was 29 per cent., when 12 hours old o per 

 cent. When the eggs were 10 hours old and the sperm 2 minutes 

 old, the average cleavage rose to 55 per cent. 



In experiment 4, n-hour-old germ cells gave 10 per cent, 

 cleavage. Eleven-hour-old eggs by moderately fresh sperm gave 

 59 per cent, cleavage. Fifteen minutes later using the same eggs 

 and sperm, only 16 per cent, cleaved. The marked reduction 

 was due again to the rapid deterioration of the sperm of the 

 second male. 



In experiment 5, the eggs of 2 females were tested by 3 different 

 males. When the germ cells were 5 hours old I per cent, cleaved. 

 When tested by moderately fresh sperm, cleavage rose to 45 

 percent. 



In experiment 6, the increased cleavage with fresh sperm was 

 57 to 73 per cent. 



In experiment 7, the small increase with fresh sperm, i. e., 

 only 1 8 per cent, and 13 per cent, respectively, was due to the 



