114 CHILDHOOD OF ANIMALS 



colours of young birds and mammals make them less conspicuous, 

 and that it may be for this reason that they have been retained in so 

 many animals, in females that have to lie hidden during the breeding 

 season, and occasionally in adults. They have not been created for 

 the purpose of concealment, but they have been retained because they 

 existed and were useful. So also the obliterating effects of counter- 

 shading, the replacement of primitive patterns by ruptive patterns, 

 and of dull colours by brilliant hues, may have come about in the 

 natural course of physiological events and been retained where they 

 were useful or harmless. 



