APPARENT EXCEPTIONS. 185 



the effect may be due to a cause which is well 

 known to be capable of producing somewhat 

 analogous results. Even before the days of Jacob 

 and of Laban, it seems to have been known, that 

 through the eyes of the female parent, colour can 

 be determined in her young ; and although this is 

 certainly not the law which commonly determines 

 colour, operating as it does, so far as we know, 

 seldom, and only in a small degree, it is quite con- 

 ceivable that, under special conditions, it is cap- 

 able of being worked as a great power in Nature. 

 But then, these conditions are not brought to- 

 gether except with a view to purpose. For now 

 let us see how this law, whatever it may be, is 

 regulated and applied. 



One thing is certain, — assimilated colouring is not 

 applied universally ; on the contrary, it is applied 

 very partially. Is it therefore applied arbitrarily — 

 at haphazard, or without reference to conditions in 

 which we can trace a reason and a rule ? Far from 

 it. The rule appears to be this : — adaptive colour- 

 ing as a means of concealment is never applied (i) 

 to any animal whose habits do not expose it to 

 special danger, or (2) to any animal which is suffi- 



