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 vitality 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 valid, 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 life 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 
1 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 Wallace. 
