EFFECTS OF AGING UPON GERM CELLS. 389 



The per cent, cleavage is a convenient and finely graded index 

 not only of the physiologic condition of the eggs at the time of 

 liberation, but at subsequent intervals. It became then a 

 simple matter to compute the rate of deterioration with age for a 

 given female, or group of females. The rate of deterioration, 

 i. e., the reduction in cleavage, in per cent, per hour, varied from 

 6.5 per cent, per hour in experiment 3, to iS.oper cent, in experi- 

 ment i, viz: 6.5, 7.0, 7.2, 8.0, 8.2 and 18 per cent, per hour, for 

 nearly comparable periods. These rates are strikingly greater 

 in Toxopneustes (from tropical waters) than in Arbacia (of the 

 temperate waters of Massachusetts). Experiments 8 and 9 

 are illustrative of the rate of deterioration in Arbacia, viz: 1.8 

 per cent, per hour, in experiment 9, 2.5 per cent, per hour, experi- 

 ment 8. When it is recalled that the difference in temperature of 

 the waters at the two laboratories is about 10 C., and the differ- 

 ence in physiologic deterioration 3 to 10 times as great, it must 

 be evident that the difference in rate is conditioned not only by 

 temperature but by differences in HO concentration, and the egg 

 protoplasm of the different species. 



The above data did not make clear whether the decreased 

 cleavage was due to the deterioration of the eggs or of the 

 sperm or both sperm and eggs. The answer to these questions 

 could be obtained in two ways: First to fertilize increasingly 

 old eggs each time with freshly liberated and tested sperm, which 

 would test the rate and degree of degeneration of the eggs. 

 Secondly to fertilize freshly liberated and physiologically good 

 eggs with fresh suspensions of increasingly old sperm, and test 

 the degeneration of the sperm. Both series of experiments were 



made. 



EFFECT OF AGE UPON EGGS. 



Aging Eggs fertilized by Fresh Sperm. Longevity of Eggs. 



Toxopneustes. 



In the following experiments, eggs and sperm aged syn- 

 chronously until the eggs either no longer cleaved or only a very 

 small per cent, cleaved. Then samples of the same eggs were 

 fertilized at each subsequent interval by freshly liberated sperm. 

 See Table IV. 



In experiment I, for example, the eggs of 4 females fertilized 



