246 PHIL RAU AND NELLIE RAU. 



Does a longer period of copulation tend to insure the fertility 

 of all the ova? or, 



Does a larger number of ova require a longer period of mating 

 in order to insure the fertility of all? 



Is there a higher percentage of fertility among the first eggs 

 deposited than among the last? (If so, the eggs retained after 

 death may not be such a waste after all.) 



At first thought one might reasonably assume that after a 

 mating of normal duration, 1 practically all of the ova would be 

 fertile. A moment's reflection tells us, however, that this is not 

 the case anywhere in the animal or plant world. But there is 

 nothing to tell us whether a shorter period of mating will result 

 in a lower percentage of fertility. One might reasonably expect 

 that in an abbreviated time the amount of sperm received into 

 the seminal receptacle would be insufficient to fertilize the normal 

 number of ova, and even more inadequate for an abnormally 

 large number. 



Whether or not such relationships exist, the following work 

 will tend to show. 



MATERIAL AND METHODS. 



The 70 insects (35 cT's and 35 9 's) which supplied the following 

 data were all isolated immediately upon leaving the cocoon, and 

 as fast as mates emerged they were placed together, a single pair 

 in a cage. Thus promiscuous mating was securely safeguarded 

 against. All of the insects were comparatively young when 

 mating began; none were over 24 hours old. 



Frequently a few eggs would be deposited before mating began, 

 but these were in all cases vigilantly destroyed. Early every 

 morning the eggs from each cage were counted and placed in a 

 vial with a cotton stopper and labeled; this comprised the ovi- 

 position of the preceding 24 hours. 



The emerging caterpillars all died in their vials. Later these, 

 as well as the empty egg-shells, were counted, and all the eggs 

 which had not hatched were dissected to find whether they were 

 infertile or whether they contained an embryo. In most cases 



1 Previous investigations have led us to conclude that, in this locality at least, 

 the species is monogamous. 



