104 PETER OKKELBERG 



to develop toward the male line when infected with the parasite. 

 The explanation offered by Smith is that the parasite causes the 

 host to elaborate a yolk substance similar to that w^hich is elab- 

 orated in the ovaries during growth of the eggs. The apparent 

 change of sex, therefore, is due to a change in the metabolism of 

 the organism. It is clear that such a change could take place 

 without the assumption that one sex is heterozygous for sex and 

 the other homozygous, as Smith has assumed. If the change in 

 the sexual condition be due to a change of metabolism in the 

 direction that he has suggested, it follows that only the males 

 should take on the characters of the opposite sex. 



i. Sex in parthenogenetic animals. The determination of sex 

 in parthenogenetic animals has been studied by various investi- 

 gators. Woltereck ('11), who worked on Daphnia, came to the 

 conclusion that there are, in each egg, competing sex substances, 

 one kind becoming active at the maturation of the egg, while 

 the other remains latent. In summing up his results he says: 



Die resultate meiner Versuche lassen sich mir verstehen, wenn wir 

 in jedem Ei verschiedene konkurrierende Geschlechtssubstanzen 

 annehmen, von denen jedesmal die eine aktiviert wird, wahrend die 

 andere latent bleibt .... die Geschlechtssubstanzen selbst 

 konnen wir uns unter dem Bilde von (latenten) Profermenten iind 

 (aktivierten) Fermenten vorstellen. 



In the rotifer Hydatina senta, A. F. S|;iull ('12) found that it is 

 decided, in the growth period of the parthenogenetic egg from 

 which the female hatches, whether it is to be a female-producer 

 or a male-producer, or, in other words, that sex is determined a 

 generation in advance. In some later experiments upon this 

 form it has been found by ShuU and Ladoff ('16) that an impor- 

 tant factor involved in the production of male-producers is the 

 amount of oxygen present in the culture, and that this probably 

 acts by increasing the rate of the physiological processes taking 

 place in the body. This conclusion is analogous to that arrived 

 at by Riddle in connection with his experiments on sex in pigeons. 

 Riddle says: " . . . the low-storage capacity of the male- 

 producing eggs as compared with the high storage capacity of the 

 female-producing eggs is therefore an index of higher oxidizing 



