SEXUAL COLOUR 89 
when the members of a species are not all 
of equal value, the less valuable will be more 
likely to be destroyed than the more valuable. 
It is as if the species, realising that it must 
form the food supply of another species and 
that certain of its members must be destroyed, 
conserved its valuable members, by casting 
its valueless ones to satisfy the enemy. 
This it does, not actively but passively, by 
so clothing the valueless that they will be 
more easily seen by the enemy and thus more 
liable to be attacked. 
As before mentioned, it does not follow that 
in every case they will be destroyed, they may 
make good their escape; but by drawing the 
attack, the valuable will be preserved from 
attack. 
Further, it is obvious that there will be a 
limit to this value marking: as, for instance, 
when males become less numerous than 
females, so their relative value will increase ; 
they are not entirely valueless. 
When they thus become of equal value as 
the female, further alteration in structure will 
cease. 
The limit to which this differentiation will 
proceed, will depend on the number of females 
a single male is able to fertilise, or his initial 
