20 



SCIENCE 



[N. S. Vol. XL VI. No. 1175 



is now in course of preparation for publication. 

 A still furtlier fact of high importance has 

 been learned from the pigeons, namely, that 

 the sexual differences of the germs persist into 

 the adult stages of the two sexes. 



been a complete lack of corroborative evidence 

 in other forms — ^the problem of the ultimate 

 basis of sex was effectively broken loose from 

 the morphological moorings which a decade of 

 increasing knowledge of the sex-chromosomes 



Cow. 



<s 



high % H=0 (?) 



■ (blood) low % fat 

 . .high metabolism 



low % H„.0 (?) 

 low fat and P. 

 j^ high metabolism 

 high % H,0 



Frog. . . 



high fat and P. 

 5 low metabolism 

 low % H^O 

 high % H,0 



(blood) high % fat 

 . .low metabolism 



(blood) low fat and P. 



(blood) high fat and P. 



low % H,0 J 



Hvdatina / c? '^ from change of food ajid increased oxygen supply. 



■^ 1 2 's from unchanged food and lesser oxygen supply. 



Daphnids { sex-intermediates, — sexual or asex. reprod. influenced by conditions. 



Moths { sex-intermediates, — quantitative germinal basis of sex. 



(blood) low % fat 



(blood) high % fat 



Again, since my first report of these results, 

 several studies by other investigators on sev- 

 eral different groups of animals, have appeared 

 which in a most gratifying manner confirm the 

 point of view of my first communication, and 

 afford further evidence for the control and 

 modifiability of sex. 



It is the purpose of this paper to arrange 

 some of the results of studies on the pigeon in 

 a diagram, upon which are properly placed 

 these various results of other investigators of 

 sex, in order to show that we are already in 

 possession of the skeleton of fact which is nec- 

 essary for a theory of sex that accords with the 

 most important fact of sex-reversal and con- 

 trol. And, that the theory of sex must be re- 

 stated — or rather may now be stated — in terms 

 that accord with the facts of sex-reversal is as 

 certain as is the fact of sex-reversal itself. 

 After our demonstration of the reality of sex- 

 reversal in doves and pigeons — even there had 



had, to a considerable extent, fastened it. For, 

 at the same time that it was proved that our 

 experimental conditions break the correlation 

 which normally certainly does obtain be- 

 tween the chromosomal constitution of the 

 zygote and the prospective sex of the aduit, it 

 was possible to identify those functional corre- 

 lations which here continue to exist (as in the 

 normal cases) and mark off the differences be- 

 tween the germs of prospectively different sex- 

 value. "We know, tiU now, of no other material 

 in which this basal persistent function has 

 been definitely identified and quantitatively 

 measured in the germ. As I have elsewhere 

 pointed out, the basic fact is that the two 

 kinds of germs are differentiated by the degree 

 or level of their metabolism. When either of 

 these two kinds of germs is forced experimen- 

 tally into the production of the opposite sex, 

 the level of its metabolism is shifted to the 

 level characteristic of the germs of that oppo- 



