384 CARL R. MOORE 



mal. In the common fowl one ordinarily considers the spurs and 

 typical feathering of the cock as secondary sexual characters due 

 to some influence of the testicle. Pezard has shown, however, 

 that these are secondary sex characters of the cock only because 

 the development of these structures has taken place in the ab- 

 sence of an ovary. A castrated cock or an early spayed pullet 

 develop the typical cock feathering and spurs as do normal males, 

 hence their presence does not depend upon a secretion of the tes- 

 ticle. They are potential characters of both sexes and their 

 absence, normally, in the female is due to some effect of the ovary. 



Steinach has neglected fundamental conditions of this char- 

 acter in arriving at his general conclusions. Thus when a testicle 

 was grafted into a spayed female rat (or guinea-pig) and the ani- 

 mal became relatively heavier than other females, Steinach claims 

 the results point to an effect of the testicle secretion and uses it 

 as partial proof of the masculinization of the female animal. 

 However, the relative increase in weight is due only to the re- 

 moval of the influences of the ovary and not to any influence of 

 the testicle, for the testicle has no influence upon the growth 

 curve. This character is comparable to spurs and cock feathering 

 in the fowl which are also not affected by the presence or absence 

 of the testicle, and I suspect that the same is true in regard to 

 weight in the guinea-pig.^ 



There appear to be not more than two distinctive somatic char- 

 acters of a male or female guinea-pig that are capable of modi- 

 fication by sex-gland transplantation. These are, (a) the teats 

 of the mammary glands and, (6) the configuration of the external 

 genitalia. Rudimentary teats are present in both animals and 

 remain in an undeveloped condition in both the normal male and 

 the spayed female. In the normal female the teats grow as sexual 

 maturity is reached and undergo considerable hypertrophy during 

 pregnancy, and as Steinach's and my own experiments show, 

 they will increase in size in a castrated male animal in which 

 ovarian grafts are growing, until they reach the size of those of a 

 pregnant female. This somatic modifying power of the ovary is 



* Experiments are now under way to determine the effect of castration and 

 spaying in the guinea-pig, in reference to its growth curve. 



