DEPARTMENT OF EXPERIMENTAL EVOLUTION. 127 



ing which will enable the rats to be fully tested before the age of the high 

 incidence of tuberculosis. 



"The table following gives some idea of the number of tests made in getting 

 evidence as to the relative intelligence displayed by the offspring of alcoholized 

 and of non-alcoholized rats." 



Insufficient funds have prevented the continuance of the experiment 

 on the modification of the germ-plasm by extremes of atmospheric 

 conditions. Meantime the plant is being maintained in good condi- 

 tion for future use. Even though we may have doubts of getting 

 positive results, still, in view of the assurances of other biologists that 

 they have gained modifications by this means, it is eminently our work 

 to make the trial. 



THE SIGNIFICANCE AND CONTROL OF SEX. 

 SEX IN BIRDS. 



To this Station seems to have fallen the opportunity of demonstrat- 

 ing that the current view that sex is determined solely by the sex- 

 chromosome is too narrow. It is chiefly Riddle who is developing this 

 field. A summary of his results were presented before the American 

 Society of Naturalists at the Columbus meeting and has been recently 

 published in the American Naturalist under the title: "Sex control 

 and known correlations in pigeons." In this is set forth 10 fines of 

 evidence that the inherent tendencies of the fertilized egg in respect to 

 sex may be altered by other factors. Riddle's chemical studies on 

 eggs destined to produce males or females, together with a review of the 

 literature, have led him to the conclusion "that sex-control, in the 

 several forms in which it has been accomplished, has been accompfished 

 fundamentafiy by the same means in all — a changed metabofism, in 

 which a higher water-content of germ and higher metabolism for male 

 production, and lower water-content and decreased metabolism for 

 female production have been definitely shown to be associated in a 

 number of instances." He concludes: 



"The studies that have thus far been made on sex, and on the experimental 

 control of sex, in pigeons go very far, we beheve, towards an adequate demon- 

 stration that germs prospectively of one sex have been forced to produce an 

 adult of the opposite sex; that germs normally female-producing have, under 

 experiment, been made to develop into males; and that germs which were 

 prospectively male-producing have been made to fomi female adults. That 

 neither selective fertilization, differential maturation, nor a selective elimina- 

 tion of ova in the ovary can account for the observed results. Further, and 

 perhaps of more importance, these studies throw much new light on the 

 nature of the difference between the germs of the two sexes. This difference 

 seems to rest on modifiable metabolic levels of the germs; males arise from 

 germs at the higher levels, females from the lower; and such basic sex-differ- 

 ences are quantitative rather than qualitative in kind." 



Of special interest, as demonstrating the chemical basis of sex, is a 

 paper published by Riddle and Lawi'ence, Sexual differences in the 



