BUTTERFLIES 71 



confined to animals, for among ourselves the power 

 of pretending to be other than what we really art 

 is often of the greatest possible service to us. For 

 example, the success of a detective largely 

 depends on his being able to pass himself off as 

 something else and to entirely conceal his real 

 calling. 



There is an old view which holds that colours 

 are due to the direct action of the sun, but this 

 will not explain the constancy of colouring in most 

 species, or the bright colours of butterflies in 

 climates such as our own. There are some 

 cases, however, in which differences in temperature, 

 at any rate in the season of the year, appear 

 to have had a distinct influence on colour, the 

 best known examples being the common continental 

 butterflies Vanessa levana and Vanessa prorsa and 

 the English butterfly Pieris napi* 



Colour is perhaps in part a matter of indifference, 

 and a part may be red because there is no reason 

 why it should be otherwise. The red colour of 

 blood, the red colour of many deep sea animals, the 

 blue colour of the sky, and perhaps the green colour 

 of the grass and vegetation generally, may, for all we 

 know, be indifferent. 



The Senses of Butterflies. Our knowledge of this 

 very interesting subject is at present very imperfect. 

 We know that the sense of smell must, at any rate 

 in some forms which have a liking for dead and 

 decaying animal matter, be very acute. The eyes 



* For a full account of these see paper on "Environment," 

 p. 34. ED. 



