THE USES OF COLOUR 19 



radiant heat is favoured by the dark colours of 

 northern insects, and it is in every way probable that 

 they are benefited by the warmth received in this way. 

 We cannot, however, as yet assert that such dark 

 colours are not also advantageous for concealment or 

 some other purpose. 



The white appearance of Arctic birds and mam- 

 mals must be advantageous for concealment in a region 

 so largely covered with snow, but it is very probable 

 that advantage is also secured by checking the loss of 

 heat through radiation. 



Thus Lord Walsingham's experiments and con- 

 clusions seem to prove that colours are sometimes 

 of direct physiological value to animals, although a 

 great deal more work must be done before we can 

 safely estimate the proportion which this advantage 

 bears to others also conferred by the same colours 

 (see also pages 92-104). 



2. Protective and Aggressive Resemblance 



By far the most widespread use of colour is to 

 assist an animal in escaping from its enemies or in 

 capturing its prey ; the former is Protective, the latter 

 Aggressive. It is probable that these were the first uses 

 to which non-significant colours were put. The re- 

 semblances are of various kinds ; the commonest cases 

 are those of simple concealment. The animal passes 

 undetected by resembling some common object which 



