208 THE COLOUKS OF ANIMALS 



tails and adjacent parts to a head in Thecla has been 

 long known : it was first observed by Dr. Arnold in 

 the case of a foreign species (Thecla larbas), and was 

 confirmed by Dr. Forsstrona in other species. The 

 fact is quoted by Kirby and Spence under ' Means of 

 Defence of Insects,' but the interpretation offered, that 

 the insects ' perhaps thus perplex or alarm their 

 assailants,' hardly expresses the true significance of 

 the character. 1 



The same fact was independently discovered by 

 Mr. E. C. L. Perkins in 1888, and this keen naturalist 

 at once perceived the meaning of the character to 

 divert the attention of an enemy towards a non-vital 

 part. The discovery is of especial interest because it 

 was made upon an English species (Thecla W-album), 

 and because Mr. Perkins tested his explanation by 

 finding that this part had been torn in a considerable 

 proportion of the butterflies. 



The observation renders it extremely probable 

 that the slender ' tails ' which occur in the same 

 position in many ' Blues ' (Polyommatus), and the 

 bright colours and eye-like spots which are often 

 associated with them, have a similar meaning. The 

 'Blues,' when resting on a flower, have the same 

 habit of moving the hind wings, as I have often ob- 

 served in our common English species which are 

 without ' tails.' The movement is such as would 

 render the ' tails ' prominent and antenna-like if 



1 Kirby and Spence, People's Edition, 1867, p. 423. 



