EFFECTS OF AGING UPON GERM CELLS. 385 



showed no change in rate and the other 4 did not form mem- 

 branes after the first observation. 



At this point the question arose whether the inability to 

 form membranes was due to the sperm or to the egg or to both. 

 The matter was tested as follows: after eggs and sperm of the 

 same age no longer formed membranes, the eggs were fertilized 

 by fresh sperm, and vice versa, freshly liberated eggs were 

 tested with old sperm. In the first case, i. e., stale eggs fer- 

 tilized by fresh sperm, fertilization membranes reappeared, and 

 were formed in most instances as rapidly as in previous matings. 

 For example, in experiment 3, membranes ceased to appear 

 when both germ cells were 23 hours old. When 24 hours old, 

 the eggs were fertilized by 4-hour-old sperm, and membranes 

 appeared in 3 out of 7 females. The eggs of 2 females formed 

 membranes in 2^ minutes each, which was more rapid than 

 when the eggs were 18^2 hours old. The third formed mem- 

 branes in 6 minutes. These observations showed that the first 

 inability to form membranes was not due to the absence of mem- 

 brane-forming substance in the eggs. 



When fresh sperm was used with eggs 42, 48, 65 and 70 hours 

 old, no membranes were formed. This showed that at this age 

 the lack of membranes was now due to a change in the eggs 

 which began about 24 hours after liberation in some females, 

 and in 42 hours in other females. The membrane substance was 

 gone. 



In the reverse experiments, when increasingly old sperm was 

 used to fertilize fresh eggs, membranes were formed as rapidly 

 and as extended from the surface of the egg as when fresh sperm 

 was used (within certain limitations). For example in experi- 

 ment 4, 23-hour-old sperm caused membranes to appear in 7, 

 3, 3, 3 minutes in the 4 females. In experiment 5 the sperm 

 which was 45^ hours old formed membranes in 2 of the 3 

 females in 2 and 2^/2 minutes respectively. In experiment 6, 

 when sperm was 73 hours old, membranes appeared in 2^, 4, 4^ 

 and 5 minutes respectively. Even when sperm was 95 hours old 

 (experiment 6) one out of 4 females formed membranes in 2^ 

 minutes. 



These and other facts clearly show that the rate and charac- 



