HETEROGONY AND TAXONOMY 215 



indicates that such growth-mechanisms can be quite markedly 

 modified should biological need arise. 



We meet with a precisely similar state of affairs in regard 

 to other biological rules. For instance, there is an undoubted 

 tendency for secondary sexual characters acquired by one sex 

 to be transferred, in whole or in part, to the other sex, even 

 if of no biological value in the other sex. But this general 

 tendency is constantly being modified or overruled by other 

 agencies, e.g. the need for protective coloration in certain 

 female birds frequently inhibits the transference of male 

 display characters to the females, and the tendency can only 

 manifest itself, among females of these groups, in those species 

 which are not in need of protection as regards colour, because 

 they nest in holes (e.g. tits, red-breast). 



Doubtless, as well as such total exceptions to Lameere's 

 rule, we should also find many minor modifications, revealed 

 by organs whose relative size was not precisely what should 

 be expected on an embracing formula, though in part a function 

 of absolute body-size. But to detect these we should have to 

 make quantitative studies of the variation of relative organ- 

 size (a) within the individuals of the several species, (b) among 

 the species of the genus ; and this has not yet been attempted. 



The undertaking of this task in insects and Crustacea should 

 be all the more interesting, since in regard to relative brain- 

 size in mammals, Lapicque (1907, 1922) and Dubois (1914, 

 1922) and Klatt (1921) have established the remarkable fact 

 that different formulae apply to the infra-specific and inter- 

 specific variation respectively. Variation of body-size within 

 the species (e.g. in different breeds of dogs or rabbits) has 

 less effect on absolute size (though more on relative brain-size) 

 than does variation of body-size from one species to another. 

 In both cases the formula y = bx k is followed, but whereas 

 the value of the growth-partition coefficient (k) of the brain 

 is 0-56 when different species are considered, it is only 

 0-22 for different-sized individuals of the same species. In 

 this particular case, the facts are doubtless to be correlated 

 with the artificial nature of the intra-specific selection that 

 has been at work. Man has been concerned to produce large 

 or small breeds, irrespective of their general adaptation or 

 their efficiency in a state of nature. The changes in absolute 

 brain-size produced by such changes in body-size are presum- 

 ably the minimum to be expected as automatic or secondary 

 result of the change in body-size ; while those found as 



