THE USES OF ANIMAL COLOR. 537 



this way. We can not, however, as yet assert that such dark colors 

 are not also advantageous for concealment or some other purpose. 



The white appearance of arctic birds and mammals 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 conclusions seem 

 to prove that colors 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 colors. 



By far the most wide-spread use of color 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 colors were put. The re- 

 semblances are of various kinds ; the commonest cases are those 

 of simple concealment. The animal passes undetected by resem- 

 bling some common object which is of no interest to its enemies or 

 prey respectively, or by harmonizing with the general effect of its 

 surroundings ; the former is special, the latter general resem- 

 blance, and both may be protective or aggressive. Among the 

 most interesting special aggressive resemblances are the cases of 

 alluring coloring, in which the animal, or some part of it, resem- 

 bles an object which is attractive to its prey. 



Mimicry is in reality a very important section of special resem- 

 blance. The animal gains advantage by a superficial resemblance 

 to some other, and generally very different, species which is well 

 known and dreaded because of some unpleasant quality, such as a 

 sting or an offensive taste or smell, etc., or it may even be pro- 

 tected from the animal it resembles : this is protective mimicry. 

 When, however, the animal resembles another so as to be able to 

 injure the latter or some other form which accompanies it or is 

 not afraid of it, the mimicry is aggressive. . . . 



When an animal possesses an unpleasant attribute, it is often 

 to its advantage to advertise the fact as publicly as possible. In 

 this way it escapes a great deal of experimental " tasting." The 

 conspicuous patterns and strongly contrasted colors which serve 

 as the signal of danger or inedibility are known as warning colors. 

 In other cases such colors or markings enable individuals of the 

 same species easily to follow those in front to a place of safety, or 

 assist them in keeping together when safety depends upon num- 

 bers. It is these warning colors which are nearly always the 

 objects of protective mimicry. 



Finally, in the highest animals, the vertebrata and many of 

 the most specialized invertebrate groups, we have some evidence 

 for the existence of an aesthetic sense. Darwin believed that this 



