SEX DETERMINATION 0.5 1 



ary sex differences in mammals and birds upon the presence 

 of the gonads acting through secretions (hormones) is clearly 

 shown by the experimental work of Steinach and Goodale. 

 The former castrated immature male rats and guinea- i)igs 

 and then introduced into the bodies of the castrated males 

 ovaries of the female of the same species. The transplanted 

 ovaries became established and caused remarkable changes 

 in the castrated animals. Their mammary glands, which are 

 rudimentary in the male, became greatly enlarged. The 

 body remained small as in females and the fur soft. Their 

 behavior too was more like that of females than of males. 



Goodale (1916) performed a similar experiment on male 

 brown Leghorn chicks with like results. (See Fig. 155.) 

 Goodale (1911% 1913) found also that mere removal of the 

 ovaries from female birds (hens and ducks) causes them to 

 assume, to a considerable extent, the quite different appear- 

 ance of males and that castrated males fail to develop many 

 of the normal male characteristics. It is accordingly clear 

 that some secretion of the ovary normally acts as an inhibitor 

 against the development of male plumage in birds, and that 

 in males a secretion of the testis is necessary for full develop- 

 ment of the secondary sex characters. 



Morgan has shown that what in female fowls acts as an 

 inhibitor to the development of male plumage is not a secre- 

 tion of the egg-cells proper but a secretion of certain "luteiil 

 cells" normally present in the ovary. He finds that in Se- 

 bright bantams, which breed has hen-feathered males, 

 "luteal cells" are present in the testis of males as well as in 

 the ovary of females. Consequently when Sebright bantam 

 males are castrated they become ** cock-feathered," that is 

 they grow the long tail-feathers and the hackle feathers 

 characteristic of males in other breeds of fowls. In crosses 

 of Sebright bantams, in which the cocks are hen-feathered, 

 with black-breasted game bantams, in which the cocks are 

 normal, Morgan found that hen-featliering behaved iis a 

 non-sex-linked dominant character probably involving two 

 distinct genetic factors. 



