196 THE COLOUES OF ANIMALS 



considered here, all the similar forms possess unplea- 

 sant attributes although they may possess them in 

 different degrees. 



The remarkable likeness between many of the 

 species of Burnet Moths (Zygaenidae) is probably due 

 to arrested divergence. They are all conspicuous 

 black and red moths, and some of them are known 

 to be nauseous. 



The unpleasant qualities may be concentrated in special 

 parts, which are so placed and coloured as to attract 

 the attention of enemies 



In certain cases the warning appearance is of a 

 different kind. The organism possesses a highly 

 conspicuous feature to which the attention of an 

 enemy is directed ; if seized, the structure breaks off 

 without harm to the animal, but with very unpleasant 

 results to the enemy. It is probable that this method 

 of defence will be found to be wide-spread. 



The defensive value of ' tussocks ' 



Only recently, in the summer of 1887, this ex- 

 planation of the beautiful flat-topped tufts of fine 

 hairs, called 'tussocks,' which occur on certain cater- 

 pillars, was shown to me by the results of an experi- 

 ment. 1 The tufts are often light-coloured, and are 



1 Trans. Ent. Soc. Lond. 1888, pp. 589-91. 



