42 



WARM. 

 A 0. of Eggs. Male. female. Ratio of Male : Female. 



1393 507 880 1:1.7 



Number of eggs at eacli lajang, 3.6. 



At the higher temperatures it coumlonl.^■ happened that the eggs were 

 developed so rapidly that the bod}' of the animal was entirely filled from 

 one end to the other, the head appearing as a smalliwint, the intestine 

 so compressed as to be scarcely Aisible. In this condition the animal is 

 unable to move and soon perishes. At the higher temperature, therefore, 

 a larger number of eggs are produced so rapidly that the body can not 

 properly nourish them. It seems to me that von Malsen's conclusions 

 should be accepted with much reserve, because of certain probable sources 

 of error. In the first i^iace he seemed to have based his estimate of males 

 and females upon the size of the eggs alone, the large ones representing fe- 

 males, the smaller eggs males. From the very marked variation in the size 

 of the female eggs, as given from his own measurements, it would seem that 

 size alone would not be a strictly accurate method of determining the 

 sexes. In the second place it does not seem improbable that, at higher tem- 

 peratures, and with a more rapid generative activity, fewer smaller eggs 

 would fall as prey to the larger eggs ; for in these animals the larger 

 female eggs are frequently nourished at the expense of the smaller. If the 

 nutritive activity of these large eggs is increased proportionately to the 

 sexual activity by higher temperature, then the larger eggs should consume 

 the smaller ones in like ratio : but von Malsen does not seem to have shown 

 this to be true. It may be said that at lower temperatures the larger 

 female eggs have relatively more time in which to consume the smaller, 

 hence fewer small, or male, eggs are laid. The question then arises, does 

 von Malsen's experiments prove that higher temperature leads to the produc- 

 tion of more female than male eggs from the generative tissue? or merely 

 that, at a higher temperature, ot the relatively larger number of eggs 

 produced, a proportionately smaller number of male eggs is consumed in 

 the nutrition of the female eggs. 



The researches of Issakowitsch upon a daphnid bring us face to face 

 with a different class of data. This author reared thi^ descendants of 

 parthenogenetic females through several generations (six as a maximum), 

 and found that the production of females is i)aralleled with high tempera- 

 ture (24° C). and that the males with lower temperature, the direct 



