REPRODUCTION AND SEX 495 



lessened or annulled by the implantation of other reproductive 

 organs, which need not be of the same sex, nor inserted in their 

 proper place. The influence is chemical, for injection of gonadial 

 extract is sometimes effective, and in some cases an implanted organ 

 develops only interstitial tissue, but no germ-cells. Extracts of the 

 brain and spinal cord of mammals in heat may produce on castrated 

 animals effects comparable to those that follow the introduction of 

 gonadial material. The influence of the hormones seems to be in 

 great part indirect, through the nervous system. 



Not a few experiments, especially on insects, show that changes 

 of environment may affect the expression of the accessory sex- 

 characters, and may indeed change them to those of the opposite 

 sex. An environmentally induced change of metabolism brings 

 about the activation of the normally latent accessory sex-characters 

 of the opposite sex, or (in males especially) prevents the activation 

 of the normal sex-characters. In some cases the gonads are markedly 

 influenced by the environmental change, so that part of the result 

 on the body may be a castration-effect; in other cases the gonads 

 are not affected at all. Kammerer attaches much importance to 

 cases where masculinised females had offspring which were all 

 masculoid — the females as well as the males. He concludes that sex- 

 characters react to the environment just like ordinary somatic 

 characters, and he believes that in both cases there is some measure 

 of transmission of the induced modifications. 



SEX-CHARACTERS AND SPECIFIC CHARACTERS.— Tandler 



and Kammerer have done good service in showing that sex-char- 

 acters behave hke ordinary specific characters, e.g. in inheritance, in 

 regeneration, and in their relation to environmental influence. We 

 think, however, that they have exaggerated a useful idea, so that 

 in its generalised expression it becomes untenable. Tandler says: 

 "All secondary sex-characters were, indeed, at first specific char- 

 acters . . . and not primarily associated with the genital sphere." 

 Thus the milk-gland has doubtless arisen from a group of skin -glands, 

 common to both sexes. Later on, in the female, it came secondarily 

 into the service of the offspring-nourishing function, and under the 

 influence of the reproductive organs. It is the enigma of its repre- 

 sentation in the males that has led to the theory that the mammary 

 gland was originally common to both sexes and not nurtural. 



In Bovidae the possession of horns is a constant character of a 

 given species or variety. They are present in both sexes. The shape- 

 differences between them form the sex-character. When there is 

 early castration in calves of a horned race, the two sexes develop 

 the same kind of horn, which bears a marked resemblance to the 

 ancestral type of Bos primigenius. 



According to many authorities, antlers began as variations on 



