2l6 BENJAMIN H. GRAVE. 



experiment that they vary greatly in their longevity. The eggs 

 of some individuals are much more vigorous and survive for 

 longer periods than those of others. The poorest lots of eggs 

 fragment in from six to nine hours, and the best lots remain 

 apparently normal from fifteen to twenty-two hours. The 

 average lot of eggs begins to fragment at the end of nine or ten 

 hours and 90 per cent, of them have fragmented after fifteen 

 hours. We may say therefore that the average longevity of the 

 unfertilized egg, during which normal fertilization is possible, is 10 

 to 12 hours. When using eggs older than these one may look for 

 a considerable percentage of abnormal embryos. It is only the 

 best lots of eggs which give normal development of all embryos 

 when more than ten or twelve hours old although early cleavage 

 may appear normal. 



The average life of the sperm in the most dilute suspensions 

 capable of giving 100 per cent, fertilization (1/6000 to 1/8000%) 

 is 4 to 5 hours. The extremes are 3^ to 18 hours. If fresh eggs 

 are added to these dilute sperm suspensions after nine or ten 

 hours from forty to fifty per cent, of fertilizations often occur. 

 On the average one can expect only 20 to 40 per cent, of fertili- 

 zations after nine hours and sometimes none at all. After ten 

 hours they may fertilize from one to ten per cent, of the eggs. 

 It was noted that abundant normal larvae developed from eggs 

 that were fertilized by these aging spermatozoa up to nine or ten 

 hours. 



A sperm suspension of 1/500 to 1/750 % lives longer than the 

 more dilute suspensions mentioned above. They may give 100% 

 fertilization up to 9 or 10 hours and a considerable percentage of 

 the spermatozoa may live for 12 hours. It was observed that 

 they usually fertilize from one to five per cent, of the eggs from 

 fifteen to twenty five hours. It is therefore apparent that the 

 conditions existing in a concentrated sperm suspension are not the 

 same as in more dilute suspensions. 



The evidence goes to show that half of the spermatozoa that 

 are shed into sea water under natural conditions die within five 

 or six hours and that nine tenths of them die within ten hours. 

 After a few hours most of the spermatozoa stop swimming and 

 lie quietly except for a few lashings of the tail at intervals. In 



