SEX DETERMINATION — A SUGGESTION. 7 



Not only are there difficulties in the way of accepting the 

 X chromosome unreservedly as the sex determiner, but many 

 facts seem to point to the general metabolism as the basis of 

 sex determination. In Rotifers 8 , for example, recent work 

 has shown that a change of sex in the offspring can be brought 

 about by controlling the food supply and oxygen supply of 

 the parents. In Daphnids 9 , food and temperature have been 

 shown to affect the sex of the offspring : the same is true also 

 in canaries. 10 Then in pigeons, Riddle 11 found that 

 normally a male-producing egg has a smaller yolk and a higher 

 water content than a female-producing egg, and that under 

 conditions of overwork the eggs produced have successively 

 larger yolks, while at the same time the percentage of females 

 is steadily increasing. Hertwig 12 has shown that by delaying 

 fertilization of the eggs in Frogs, a large percentage of males 

 results, and it is probable that this is correlated with the 

 absorption of water by the unfertilized eggs. King 13 has 

 shown that by desiccating frogs' eggs a majority of females 

 is obtained. In all these cases a changed metabolism in the 

 parents or their germ cells influences the sex of the offspring ; 

 out of course, in all, there is the possibility that the changed 

 metabolism brings about selective maturation and so only 

 affects the sex of the offspring through its chromosome content. 

 Riddle's evidence against this is, however, very strong. Again, 

 Geoffrey Smith's 14 work on parasitism in crabs points even 

 more clearly to the type of metabolism as the basis of sex- 

 determination ; a change in sex being effected during the 

 lifetime of certain individuals, seemingly due to the change 

 in their metabolism brought about by the parasites which 

 infect them. Baltzer 15 has shown, that in BoneUia, larva) 

 which develop attached to the proboscis of the female develop 

 quickly into males, whereas those which remain in the mud or 

 sand grow slowly, and eventually become females. This 

 also seems a clear case where the general metabolism deter- 

 mines the sex, and not any given chromosome content. 



