58 INANITION AND MALNUTRITION 



Whitney ('08) likewise obtained negative results with Hydatina senta. 

 Temperature has no influence upon sex-determination (versus Maupas), and 

 "starving the young females for the first few hours after they hatch does not 

 cause them to produce a higher percentage of male eggs." 



Shull ('10, 'n) after careful and extensive experiments upon Hydatina 

 senta concluded that while sex-production is dependent upon both internal and 

 external factors, the quantity of food probably has no influence in this respect. 

 Starvation may be accompanied by an increased proportion of parthenogenetic 

 male-producers, but this is probably only an indirect effect, due to a decrease in 

 certain substances incidentally introduced by the food. Thus the question as 

 to the effect of nutrition upon sex-production in rotifers still remains somewhat 

 uncertain. 



ARTHROPODA 



In the phylum Arthropoda, the effects of inanition have been studied most 

 extensively in the class Insecta. There have also been numerous observations 

 upon the Crustacea, and a few on the Myriapoda and Arachnida. 



Crustacea. — The investigations in this class have included both the sub- 

 classes, Malacostraca and Entomostraca, and those in the latter group will be 

 considered first. The Entomostraca, like the rotifers, have attracted attention 

 on account of the apparent effect of inanition upon sexual reproduction. Leydig 

 included the water flea Daphnia among the forms in which sex is determined by 

 external factors, including nutrition. Kerherve ('92) claimed that Daphnia 

 magna is parthenogenetic during abundant nutrition, but is quickly transformed 

 into sexual reproduction by unfavorable conditions, especially by inanition. 

 Cuenot ('94) noted a similar condition in Moina rectirostris. Issakowitsch 

 ('05) in Simocephalus vetulus found that sexual reproduction is induced during 

 the asexual stages by either low temperature or inanition. Woltereck ('08, 

 '09, '11) admits the hereditary cycle in daphnids, but claims that in Daphnia 

 longispina a peculiar variety of different body form is produced by unfavorable 

 environment, chiefly by malnutrition. The effects of environmental factors 

 apparently may be hereditary in Daphnia longispina and in Hyalodaphnia 

 cucullaia. The external factors affect sex only in the "labile period" and then 

 only indirectly, through influence upon the internal mechanism of sex-production. 

 Finally McClendon ('10) concludes that "The life cycle of a Daphnid is therefore 

 an hereditary tendency but can be influenced by nutrition and probably by 

 temperature and the accumulation of excretions." 



On the other hand, Green ('19) has recently made careful and extensive 

 experiments upon Simocephalus vetulus, concluding that: "The sexual state is 

 probably determined in the ovary of the preceding generation. There are 

 almost certainly predisposing 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." It would therefore appear that among the Entomostraca, as already 

 noted for the rotifers, the effect of inanition upon sex-production is still an open 

 and uncertain question. 



