UNMAN REED CiRKEX. 



n only partially developed, showing the sexual capacity to 

 be gradually lost. 



(b) Parthenogenetic females, which display no tendency to 

 produce ephippial eggs. 



(c~) Males. 



The kinds of offspring occur in no definite order, but their 

 character is probably determined at birth, and not by subsequent 

 conditions. (See summaries of isolation experiments 2 and 

 3.) Eggs which will develop into males, into highly sexually 

 females, and parthenogenetic females, often arise in the same 

 female and not infrequently at the same time, either early or 

 late in her reproductive period, whether or not she has passed 

 through the sexual state herself. 



2. The sequence of the generations is very indefinite: 



(a) The stem mother is functionally like the females produced 

 parthenogenetically, except that she probably never gives rise 

 to ephippial eggs. (However see Sharfenberg, 1911, p. 24.) 

 There is not even an approximately definite number of genera- 

 tions in the cycle from one stem mother to another. It may be 

 one or many. 



(6) The remoteness of the generations from the stem mother 

 bears no definite relation to the percentage of males produced, 

 the ratio of sexual to parthenogenetic females, or to the duration 

 of the sexual state when present. 



(c) The sexual state is probably determined in the ovary of 

 the preceding generation. There are almost certainly predispos- 

 ing factors in the environment but it is not certainly known what 

 they are. Food or lack of food does not offer a sufficient explana- 

 tion. Sexual females and males tend to arise at the same time, 

 presumably in response to the same environmental complex. 



(d) Cultures are indefinitely viable parthenogenetically. The 

 species will express itself in all of its forms under a great variety 

 of conditions. Under certain conditions sexual forms are com- 

 pletely inhibited. Parthenogenesis cannot be completely in- 

 hibited in cultures or even in individual females. Thus cultures 

 of Simocephalus vetulus can never be terminated merely because 



hi- onset of sexuality. 



The production of mixed broods is not to be interpreted 



