48 Trans. Acad. Sci. of St. Louis. 



SAMIA CECROPIA. 



Table 27 presents the data of the fertility of the River 

 des Peres Cecropias coming from the normal cocoons. 



We have 9 insects recorded above which mated from 

 4 to 6 hours. A glance at the total column promptly tells 

 us that the per cent of infertility is so low that the egg 

 masses may be called practically all fertile. These pairs 

 were artificially separated after having been together 

 for 5 or 6 hours, or in one case 4 hours. 



In connection with the normal period of copulation, 

 15 to 18 hours, we have 11 insects which show the per 

 cent of infertility to be correspondingly low. On the 

 whole, this entire lot of eggs were very fertile ; the 4704 

 eggs included only 106 infertile ones, or 2.2%, while 

 97.8% of the aggregate were fertile. 



We cannot see any perceptible difference in the fer- 

 tility of the early or late deposition, but the smallness of 

 the per cent of the infertile eggs in the total deposit 

 would make it an increasingly delicate task to detect 

 such a difference. This year's material shows a much 

 higher degree of fertility than that for the year 1911. 



In the total F. U. column of the table is given the num- 

 ber of eggs in which the embryo partially developed but 

 for some unknown cause died in the shell. These con- 

 stitute 3.8% of the whole number of eggs deposited, and 

 4% of the fertile eggs, a far smaller proportion than the 

 1911 eggs, which showed 11% and 14.5% respectively 

 unhatched though fertile. 



Here we see clearly that a shortened period of mating 

 does not reduce the fertility of the eggs; that the insect 

 could economize on time spent in copulation and still 

 cause no reduction in the progeny, or that in some cases 

 she might even increase the number of her offspring by 

 utilizing this extra time for oviposition, in which she 

 might otherwise be cut short. 



