HOKMONE FACTOKS IN GKOWTH AND DEVELOPMENT 199 



Notwithstanding this non-specificity we may expect that the action of 

 the same sex hormone differs in different species. In no other instance 

 are we so profoundly impressed with the importance of the condition 

 of the particular organism as regards the final effect produced by the 

 same agent. Two causes altering the susceptibility of the organisms 

 toward the sex hormonic action deserve special mention, namely, hered- 

 itary sex determination and the age of the organism. There can be no 

 doubt that the fertilized eggs of all species possesses a sexual predis- 

 position; sex is inherited according to Mendel's law as shown by the 

 sex ratio (Morgan (a)). The degree of this sexual predetermination, 

 however, is different in different species. In mammals it seems to deter- 

 mine merely whether the developing embryo shall have a male or a female 

 interstitial gland, while the further development, including that of the 

 generative sex gands, is determined by the interstitial gland (Lillie). 

 In insects, however, very little, if any, effect upon postembryonic develop- 

 ment is left to sex hormones. In butterflies, primary as well as secondary 

 sex characters are determined in the hatching caterpillar; castration or 

 even implantation of the heterologous gland into the castrated caterpillar 

 does not change the secondary sex characters of the individual (Meisen- 

 heimer, Kellog, Kopec). There are, however, no good reasons to quote 

 this instance as disproving the hormonic theory; we should not be sur- 

 prised to find the absence of sex hormones in a group of organisms in 

 which the entire system of internal secretions is present in an extremely 

 rudimentary condition, or entirely absent. In crustaceans, at least the 

 male characters seem to be controlled by sex hormones (Smith). 



Since the number of sex characters increases with age, it is clear that 

 the effect of administering or removing the sex hormones depends on the 

 age of the individual. In mammalians and birds only slight changes are 

 effected by castration in postpuberal life, while castration before puberty 

 results in profound inhibition of the secondary sex characters. If develop- 

 ment of the interstitial gland is prevented in embryonic life and the 

 embryo is supplied with the hormones of the opposite sex, an almost com- 

 plete change in the direction of the opposite sex may result (Lillie). 



The effect of the sex hormones, in most species, seems to be the develop- 

 ment of new morphological characters in both sexes. In such cases, as 

 Tandler and Grosz pointed out in regard to man and other mammals, the 

 removal of the sex hormones results in the maintenance of an infantile 

 "neutral" type, but does not lead to the development of the characters 

 of the opposite sex. In birds (Morgan (&) (c) (d), Goodale, Pezard) this 

 is true only for the male hormone, which produces the fleshy appendages 

 typical of the male, but otherwise leaves the species unchanged. The 

 female hormone, however, has a suppressing action upon many of the neu- 

 tral characters, in addition to its power of developing specific female char- 

 acters (plumage, etc.). 



