76 SEX 



functional activity to special strains, contacts, 

 and pressures, that is, to stimulation, which 

 must and does have some physiological effect 

 on their development and mode of growth." 

 To explain the restriction of sex-characters 

 to one sex, to the period of maturity, and 

 often to one period of the year, Cunningham 

 supposes that " heredity causes the develop- 

 ment 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." Unisexual characters are largely 

 of the nature of excrescences which originated 

 from mechanical or other irritation in the 

 male or the female at particular times and 

 in particular states of body. They are now 

 part and parcel of the inheritance, but they 

 are not expressed in the body except in 

 association with physiological conditions the 

 same as those under which they were origin- 

 ally produced. 



Cunningham seeks to show that sex char- 

 acters may be legitimately interpreted as the 

 hereditary outcome of special irritations. The 

 legitimacy of this interpretation depends (1) 

 on the experimental evidence that can be 

 adduced to show that callosities, excrescences, 

 proliferations, etc., do arise as the direct 

 result of stimulation; and (2) on the case 

 that can be made out, on experimental or on 

 logical grounds, for believing that somatic 

 modifications may be directly transmitted 

 in some degree at least. This raises the 

 whole question of the transmission of somatic 

 modifications, which are acquired by the 

 individual as the direct result of peculiarities 



