LIFE CYCLE OF SIMOCKI'I I A I. US VETULUS. 77 



tin- females had become asexual. The one sexual female re- 

 mained so until she had developed three ephippia. Thm she 

 developed a brood of 5 asexual females and died August 9. It 

 was not surprising to find so large a percentage of empty ephippia 

 appearing in the presence of males since the same thing occurs 

 in general cultures, though I had thought it might, in the latter 

 case, be due to too small a percentage of males. That this 

 explanation is erroneous is shown by this and the following ex- 

 periments. 



Several of the female broods obtained from the two females 

 isolated in isolation experiment number i, were placed with 

 numerous males and examined daily. On July I more males 

 were added since I noticed several incipient ephippia appearing. 

 On July 30 the culture numbered about 150 individuals, and only 

 two ephippia had fully developed, one of these being empty. 

 By August 6 there had been developed 14 ephippia, most of them 

 empty. The percentage of ephippial females thus remained 

 less than 10 per cent., so low that it is quite obvious that the 

 presence of males could not be the factor responsible for their 

 appearance, since larger proportions of sexual females often 

 occur in females which are segregated from the males. Not 

 all of the ephippia reached full size, though most of them did. 

 There was a dearth of males at no time during this experiment, 

 yet less than half of the fully developed ephippia contained 

 fertilized eggs. The fourth brood of female number 18 of isola- 

 tion experiment 3, consisted of 7 females. These when very 

 young were placed with 10 males. All seven, however, proved 

 to be asexual, although some of their offspring developed into 

 sexual females in the absence of males. 



The 20 females of the fifth brood of female number 38, of 

 isolation experiment 2, were divided into two lots, 10 being kept 

 with males and 10 without. Of the lowith males, 9 developed 

 ephippia, a few of which contained eggs when the molt was cast. 

 These eggs, however all degenerated, so presumably they had 

 not been fertilized. The males had all died at this time. Six of 

 these females became asexual after producing the first ephip- 

 pium. I placed some more males with the remaining four sexual 

 females and was fortunate enough to observe two matings of 



