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THE AMERICAN NATURALIST [Vol. XLI 



changing the nutrition, have been cited as a demonstration of 

 this point. Statistics of human births have been judged in such a 

 way as to lend some support to this view. A good review of this 

 aspect of the question has been given by Geddes and Thompson 

 (:01). The vaHdity of such conclusions has been well discussed 

 by Newcomb (:04), who has made a statistical inquiry into the 

 probable causes of sex in the human subject. Newcomb concludes 

 that the causes of sex are beyond voluntary control. 



Cuenot repeated Yung's experiments on tadpoles with contrary 

 results. Eggs from the same mother, but of different layings, 

 gave a more constant proportion of males to females than Yung 

 obtained. The ratio of males to females in the young (54.85% 

 females) did not differ materially from the ratio (61.5% females) 

 existing among the metamorphosed tadpoles found in a state of 

 nature in the vicinity of Nancy. Born ('81) found 52 per cent 

 of females in the metamorphosed tadpoles near Breslau. Gries- 

 heim ('81) found 63.63 per cent of females in young Rana tempo- 

 raria in the vicinity of Bonn. Pfluger ('81) found 64.5 per cent of 

 females in the same vicinity, and 86.8 per cent near Utrecht. The 

 percentage of old females in the latter vicinity he found to be 51.2. 

 Pfluger concluded that the sex was determined in the egg. From 

 his results on tadpoles and other animals, Cuenot hkewise con- 

 cluded that sex was not influenced by the conditions of develop- 

 ment. He decided further that there was a certain sexual ratio 

 common to the frogs of any particular vicinity, and that this ratio 

 might vary among frogs of different locahties. In view of the 

 comparatively small number of frogs observed, the last conclusion 

 may possibly be open to question. 



Von Malsen (:06) and Issakowitsch (:06), the former for the 

 worm Dinophilis apatris and the latter for Daphnia, have recently 

 reaflfirmed the statement that an abundance of food and a low 

 temperature cause a greater number of eggs to develop into females, 

 while a higher temperature and a scarcity of food result in the 

 development of a greater number of males. The food supply, 

 according to them, is the main factor in this process, nnd the 

 temperature acts only indirectly by influencing the imtriiioii. 

 It is to be remembered, however, that in experiments dealini^ with 

 a whole animal, it is difficult to exclude all causes except food and 

 temperature. 



