LIFE CYCLE OF SIMOCEPHALUS VETULUS. 83 



IKT first two broods, pure male offspring. These were followed 

 by three pure broods of females, and then a brood of 15 males. 

 The seventh brood was a mixed brood. Her last 7 broods, total- 

 ing 66, were all females. The sexual and asexual females in 

 these last broods occured in about equal number, namely, 30 

 sexual, and 36 asexual. Numberless such instances might be 

 cited to show that males often appear in the- first broods. The 

 summary of the data in isolation experiment 2 shows that the 

 first broods were pure male in 16 instances, pure female in 26 

 instances, mixed in 2 instances, and undetermined in i ; while 

 the last broods were pure male in 1 1 instances, pure female in 

 28, and mixed in 6. The tabulated results in isolation experi- 

 ment 3 are also in accord with the data just given and are, I 

 believe, quite conclusive on this point. It will be noted that 

 there is no marked increase or decrease in the number of males, 

 sexual females, or of asexual females, from the first of the sixth 

 broods, inclusive, in the descendants of the 24 stem mothers, 

 for the three generations, in either the sexual or asexual lines. 

 When the first broods of newly collected old and young females 

 are compared no difference in kind is noted, as shown in experi- 

 ment 5. When these same individuals are kept in small con- 

 tainers in the laboratory, no matter if the food supply is abund- 

 ant, if the water is not changed often, sexual forms appear in 

 the offspring of young and old alike, and in like proportions. 

 These facts point to the conclusion that there is no correlation 

 between the age of the mother and the kind of offspring. 



4. Do mixed broods indicate a transitional stage from male 

 producing to female producing and vice versa? 



The summary of isolation experiment 2 shows 9 instances of 

 the production of mixed broods which are preceded and followed 

 by broods of the same sex, while there are but four cases in which 

 mixed broods are preceded and followed by broods of different 

 sex. There are in this same experiment two cases in which the 

 first brood was a mixed brood, and 6 cases in which the last 

 brood was mixed. Quite often one mixed brood follows another. 

 I have found no evidence in favor of the view suggested by this 

 question, the occurrence of mixed broods in these experiments 

 being entirely capricious. 



