Secondary Sexual Characters 445 



that natural selection has first developed these organs as recog- 

 nition marks by means of which the individuals find each other, 

 and later the greater vitahty of the male causes them to develop 

 more fully in that sex.^ 



Cunningham has attempted to account for secondary sexual 

 characters by means of the theory of the inheritance of acquired 

 characters. His effort is to show how the theory will account for 

 these structures, the theory being assumed to be vahd, for to 

 the author it is " obvious that if the removal of the testes can affect 

 the development of tissues in the head, the development of the 

 latter may affect the properties of the testes." Such statements 

 only confuse the issue, which, after all, must rest on the experi- 

 mental proof as to whether or not the special development of 

 parts of the body does bring about corresponding changes in the 

 germ-cells. There has been no difficulty in showing that the 

 removal of the reproductive organs affects the body ; but as yet 

 little or no evidence that is satisfactory has been obtained to 

 show the converse to be true. 



Cunningham assumes that the use of the secondary sexual 

 organs often subjects them to special mechanical irritation when 

 other organs of the body are not affected. These mechanical 

 strains and pressures affect the development of the organs, and the: 

 results are supposed to be inherited. He asks, why are the secon- 

 dary sexual characters of the male restricted to the male off- 

 spring and those of the female to the female offspring? His 

 answer is that ''heredity causes the development of acquired 

 characters for the most part only in that period of Hfe and in 

 that class of individuals in which they were originally acquired." 

 The same idea is more fully expressed in the statement ''that 

 the direct effects of regularly recurrent stimulations are sooner 

 or later developed by heredity, but only in association with 



' Lameere also accepts that part of Darwin's theory of sexual selection that 

 assumes the secondary sexual differences to be due to natural selection between 

 the individuals of one sex; but rejects Darwin's idea that the differences can be 

 accounted for by selection of the males by the females. In these respects he 

 agrees with V^^allace. 



