1028 LIFE : OUTLINES OF GENERAL BIOLOGY 



with the author in feeling the necessity for psychological as well as 

 physiological interpretation. 



HEREDITY AND SEX-CHARACTERS.— The inheritance of 

 secondary sex characters has become clearer since Darwin's day. He 

 was indeed convinced that the secondary sex characters, though 

 expressed in the male or in the female only, are genetically 

 present in both sexes and are transmitted through both. He 

 referred, for instance, to the expression of masculine charac- 

 ters in old or diseased females. But in default of any know- 

 ledge of the role of internal secretions, Darwin was forced 

 to subsidiary hypotheses. There is an antique ring in sentences 

 like this: "When variations occur late in life in one sex, and 

 are transmitted to the same sex at the same age, the other 

 sex and the young are left unmodified." (Descent of Man 2nd ed., 

 1888, vol. i, p. 371.) 



What is indicated by modern experiments in castration, implanta- 

 tion, injection of hormones, as well as in hybridisation, is briefly 

 this, that a positive masculine character normally develops in the 

 somatic milieu of the male, but remains latent in the somatic 

 milieu of the female. It is either inhibited by the ovarian hormones, 

 or modified by these so that it finds feminine not masculine expres- 

 sion. That the masculine character may be potentially present in 

 completeness, is shown by the change in the plumage of ovarioto- 

 mised young females at the next moult. "If the ovary of a domestic 

 bird be removed completely, many of the secondary sexual characters 

 of the male appear. Some individuals become nearly complete 

 replicas of the male, others imperfect imitations of the male. If the 

 testes be removed, the majority of the secondary sexual characters 

 of the male develop, though a few remain in an infantile condition. 

 Castrated drakes lose the power of developing the summer plumage." 

 (H. D. Goodale, Gonadectomy in Relation to the Secondary Sexual 

 Characters of some Domestic Birds, Carnegie Institution of Washing- 

 ton. Publication No. 243, 1916, p. 51.) 



The conditions differ in different types; thus Geoffrey Smith 

 showed that the parasitic castration of male crabs of various kinds 

 by Rhizocephala may be followed by remarkable changes in the 

 somatic metabolism, as the altered composition of the blood shows. 

 Thereafter, a small ovary appears and forms ova, the abdomen 

 and its appendages put on feminine characters, and the male carries 

 its protruding parasite as if it were a bunch of eggs. While there 

 are cases of organisms which carry the factors of only masculine 

 or only feminine characters, there are certainly many cases, such as 

 the female bird or the male crab, where there is the potentiality 

 of some of the distinctive characters of the opposite sex. And these 

 latent characters may be activated by a change in the internal 



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