PROTECTIVE VALUE OF COLOUR 187 



by the possession of the earth. By their very enter- 

 prise they created competition, as in commerce to-day. 

 By the tendency of all living things to increase in 

 number beyond the means of subsistence the weaker 

 were ousted by the stronger. Those better fitted to 

 endure hunger or lack of air, cold, or heat, those 

 that could escape at such hard times to more genial 

 surroundings and hold their own against its occupants, 

 were favoured, and their offspring again selected by the 

 same process. 



Sympathetic colouration, viewed from this stand- 

 point, became a means of concealment from prowling 

 foes, or of lying in wait to surprise and capture unsus- 

 pecting prey. The stick-caterpillar, from being a 

 mere freak of nature, became a test-object for a 

 definite experiment ; and Darwin, never satisfied until 

 he had raised a point of view to an assured conclusion, 

 tested the value of his hypothesis by bringing such 

 caterpillars, both singly and on their food-plants, 

 into an aviary. The result was encouraging. The 

 birds greedily devoured the isolated caterpillars and 

 failed to find those on the plants. 



More recently the same experiment has been 

 carried out with mantis. Two varieties, brown and 

 green, were chosen, and forty of each variety attached 

 in open ground by a similarly coloured thread to 

 plants of sympathetic and contrasting tints. At 

 the end of a fortnight all those which had been tied 

 to plants of a colour similar to their own were well 

 and vigorous, while those contrasting with their 



