FERTILITY OF CECROPIA EGGS. 249 



Furthermore, it is found that when the percentages of fertility 

 of each day's deposit are calculated, in two thirds of the indi- 

 viduals the fertility increases as the days go by, w T hile in only 

 one third is there a decrease. Hence we are forced to admit 

 another heavy loss; for this evidence would lead us to conclude 

 that a large proportion of the eggs retained after death were also 

 probably perfectly good. 



In the material here considered we find also no correlation 

 between this phenomenon and the long or short duration of 

 copulation. 



The table shows that in some of the cases of prolonged mating, 

 the first day's deposit of eggs contained a great number which 

 were infertile. Why this should be has not been ascertained. 

 Being confident that all eggs laid previous to mating were 

 destroyed, we are at a loss to explain why the first eggs, which 

 one would think had the best opportunity of being fertilized, 

 were otherwise. But a stranger fact still is that w r hile female 

 29 was in copulo 24 hours, not one egg was fertile, and almost 

 the same condition existed in females 24, 28 and 30. 



One might think that those insects which carried an abnormally 

 large number of eggs would have less chance for their complete 

 fertilization. According to the data in our table, however, no 

 such relation is found to exist. In fact the high percentage of 

 fertility in many of these cases might suggest that the vigorous 

 condition of the female contributed more toward insuring the 

 fertility of the eggs than did the amount of sperm or the duration 

 of copulation. 



In all of the eggs in these experiments, then, 77 per cent, were 

 fertile and 23 per cent, infertile. In the next to the last column 

 of the table is given the number which partially developed but, 

 from some unknown cause, died in the shell before hatching. 

 These constitute 14.5 per cent, of the fertile eggs, or n per cent, 

 of the whole number deposited after mating. All of the eggs 

 were kept under identical conditions, so if 85.5 per cent, of the 

 fertile ones hatched, the fact that these 14.5 per cent, did not 

 hatch can not be attributed to environmental conditions. 



Some of the eggs are laid in closely adhering clusters, and some 

 are dropped singly. It was suspected for a time that the cater- 



