41 



the conclusion that the sex is not determinorl by external conditions. While 

 the preponderance of evidence along this line seems to argue strongly 

 against any influence upon sex -determination by food conditions, yet there 

 is one case, that of Hydatena senta and the daphnid, Simocephalus, investi- 

 gated by Nussbaum and others, in which it seemed probable that food 

 might have some determining influence. JNIaupas, on the other hand, re- 

 garded temperature and not food as the influential factor. In this con- 

 nection, the studies of von Malsen (Archiv. f. mikr. Anat., 69: 63-97, 1906.) 

 upon a small worm, Dinophilus apatris, and of Issakowitsch (Idem) upon 

 daphnids, are of especial interest. Von Malsen found that a higher tem- 

 perature (26^ C) was favorable to the development of males, while a lower 

 temperature gave an increased ratio of females. He does not attribute the 

 change in the sex ratio to the temperature directly, but indirectly as affect- 

 ing tlie nutrition of the animal. The amount of food at the disposal of 

 the animal was the same, but at the higher temperature, the sexual ac- 

 tivity of the animal, i. e., the rapidity with which a large number of eggs 

 was produced, was abnormally accelerated, so that the bodily nutrition was 

 insufficient for the proper nourishment of the eggs. Consequently, at a 

 higher temperature a larger number of eggs are produced, and among 

 them is a proportionately large number of smaller or male eggs. At a 

 lower temperature, on the contrary, reproductive activity was slower, and 

 among the smaller number of eggs developed, a larger ratio of well nour- 

 ished female eggs was the result. There was more time for the develop- 

 ment of these eggs, and consequently more food placed at their disposal. 

 To estimate the value of these statements it is necessary to examine the 

 data upon which the conclusions are based. The number of eggs considered 

 and the sexual ratio in the warm and cool cultures are shown in the fol- 

 lowing tables : 



NORMAL. 

 No. of Eggs. Male. female. Ratio of Male : Female. 



1140 327 813 1:2.4 



Number of eggs at each laying, 5.6. 



COOL. 



So. of Eggs. Male. Female. Ratio of Male : Female. 



3948 973 2975 1:3.5 



Number of eggs at each laying, 4.2. 



