466 CARL R. MOORE 



or femaleness in all cases after transplantation of the gonad of 

 the opposite sex. The female increases in weight not because 

 of the influence of the secretion from the transplanted testis, but 

 solely on account of the removal of the ovary, which alone seems 

 to have any influence upon the growth of the animal. There 

 seems to be no doubt that the presence of the ovary does prevent 

 the normal ascent of the growth curve. In order to know 

 whether this sex difference in weight was due entirely or only in 

 part to the influence of the secretions of the gonads, the pre- 

 ceding experiment was carried out. The results show very 

 conclusively that there is a real difference between the capacity 

 of the two sexes to accumulate somatic materials when there are 

 no secondary influences that may be attributed to the influence 

 of the gonad. As table 2 shows, this difference has been 

 exhibited at each stage by each of the seven litters used. 



It is interesting to consider this potential weight difference 

 of the 'determined male' and the 'determined female' in their 

 development in the light of Riddle's theory of sex.^ Riddle and 

 his co-workers have demonstrated actual differences in the 

 chemical constitution of male-producing and female-producing 

 eggs of the pigeon. He has not only shown that the female- 

 producing egg contains a greater phosphatide content and a 

 lesser percentage of water, but he has also demonstrated that these 

 chemical differences found in the dimorphic ova of birds are 

 carried over into the adult life of the bird.^ His idea is that 

 sex determination is based upon a higher rate of metaboUsm of 

 the ovum producing a male than of that producing a female, 

 and several researches are cited to show that the same relative 

 rate of metabolism persists in the adult male and female. It 

 has occurred to the writer that these basic differences in weight 

 of the two sexes of rats may also indicate a possible difference 

 in metabolism inherited from the original ovum from which 

 each had been developed. But aside from the primary differ- 

 ences that may exist in the determined male or female, the 

 secondary influences that make the female a more apparent 



^ Riddle ('17). 



® Lawrence and Riddle ('16). 



