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THE AMERICAN NATURALIST [Vol. L 



tion that in a particular mammal 99 per cent, of growth 

 power is lost before birth. In respect to "heat produc- 

 tion" or the "basal metabolism" of embryo and adult the 

 data for comparison are not extensive, but it too lends sup- 

 port to the view that this basal metabolism is higher in 

 the young than in the adult. It may be added that Ben- 

 edict and Emmes 9 have recently shown by very exact 

 measurements that the basal metabolism of men is higher 

 by about 6 per cent, than that of women. 



If a higher metabolism exists in male-producing germs, 

 and this is associated with higher water-content, as we 

 concluded in 1911, it is easy to see why a number of proce- 

 dures have since been shown to effect a control of the 

 production of sex. In 1912 Miss King desiccated toads' 

 eggs and obtained 87 per cent, of females. This was 

 the converse of the earlier experiments of Hertwig, and 

 of Kuschekewitch, who "over-ripened" frogs' eggs— a 

 process during which they were found to take up ivater— 

 and obtained, in the experiments of the latter author, as 

 many as 100 per cent, of males. I think we can now see 

 it was a shifting of the metabolism, through the agency 

 of the water values, that produced the shifting of sex in 

 the eggs of the frog and the toad. 



More recently still, Whitney has effected a change in the 

 sex of the offspring of the rotifer— Hydatina— a change 

 from female- to male-production by means which he con- 

 siders as serving to increase metabolism in the treated 

 forms. Confirmation of Whitney's conclusion that it is a 

 heightened metabolism that brings about male-production 

 is now to be had in the result obtained by Dr. A. F. Shull 10 

 who finds that an increased oxygen supply leads toward 

 an increased production of males in Hydatina. It now 

 seems clear that a heightened metabolism in the Rotifers 

 is the agency of increased male-production. 



