WHAT DETERMINES SEX? 118 



support the view that changes in nutrition 

 and other environmental conditions may 

 affect the mother so as to alter the ordinary 

 proportions of the sexes probably enough 

 by affecting the relative numbers of male- 

 producing and female-producing germ-cells. 

 Thus Issakowitsch, working with the partheno- 

 genetic females of one of the water-fleas, 

 Simocephalus, and Von Malsen, working with 

 the primitive worm-type, Dinophilus, in which 

 the ova are fertilised, found that differences 

 of temperature affected the proportions of 

 the sexes, apparently by affecting the nutrition 

 of the mothers. Both sets of experiments 

 are the more satisfactory that they seem to 

 be free from any fallacy due to differential 

 death-rate in the young of the two sexes. 



A PHYSIOLOGICAL VIEW. To the view of 

 sex, expounded in The Evolution of Sex in 

 1889, a reference must again be made, for we 

 find ourselves unable to get away from the 

 conviction that there is no sex-determinant 

 or factor at all, in the morphological or in 

 the Mendelian sense, but that what settles 

 the sex is an initial difference in the rate or 

 rhythm of metabolism. This may also be 

 expressed as a difference in the relation of 

 nucleoplasm and cytoplasm, as well as in the 

 ratio of anabolism to katabolism. 



According to this view, the deep consti- 

 tutional difference between the male and the 

 female organism, which makes of the one a 

 sperm-producer and of the other an egg- 

 producer, is due to an initial difference in the 

 balance of chemical changes. The female 

 seems to be relatively the more constructive, 

 H 



