350 riddle: control of sex ratio 



A glance at the diagram indicates three other groups of ani- 

 mals which experimental work has thrown into the general ques- 

 tion of the control of sex. The information at hand for these 

 forms does not so expressly concern the egg as does that from 

 the preceding cases, but all of these latter groups are concerned 

 with early stages — some of them with the generation preceding 

 the egg whose sex seems influenced by conditions. The results 

 of studies of the first of these groups — Hydatina — are of such a 

 kind as to show that they are in general accord with the meta- 

 bolic differentials of all of the previously mentioned cases of sex- 

 control. One can scarcely doubt that change of food and in- 

 creased oxygen supply are consonant with increased metabolism, 

 just as the studies of Whitney ('14 and later) particularly, and 

 later of Shull ('16), have shown that these changes lead to the 

 production of male-producing daughters. 



The second of these groups — the Daphnids — have been stud- 

 ied by three independent investigators who agree upon two 

 points that are of importance in the question of the control of 

 sex, and to the general theory of sex as stated here, though the 

 results throw little light on precisely what is causally involved. 

 Issakowitch ('05), Woltereck ('11), and Banta ('15) all find 

 numerous sex-intergrades in a material in which all agree that 

 the type of reproduction — sexual or asexual — is influenced by 

 environmental conditions. All further agree that "unfavorable 

 conditions" (or is it a change from favorable conditions?) tends 

 toward sexual reproduction, while "favorable conditions" favor 

 asexual reproduction. 



In the third of these groups — the moths — the studies of Gold- 

 schmidt ('12, '14), Goldschmidt and Poppelbaum ('14), Harri- 

 son and Doncaster ('14), and the work of Machida, have dem- 

 strated again sex-intermediates of various grades. Moreover, 

 it has been shown that from among the various geographical 

 races of moths certain matings can be arranged which produce 

 rather definite types of male- or female-intermediates — or sex- 

 intergrades as Goldschmidt elects to call them. And further, from 

 pairs involving still other species still other levels or grades of 

 sex-intermediates may be -freely obtained. A more or less fac- 



