AGGRESSIVE RESEMBLANCES, ETC. 75 



Mr. Wood-Mason to Mr. Wallace, who kindly lent it 

 to me. 



Another beautiful example of Alluring Colouring 

 was discovered by Mr. H. 0. Forbes in Java. Butter- 

 flies are often attracted by the excreta of birds, and a 

 spider (Ornithoscatoides decipiens) takes advantage of 

 this fact to secure its prey. The resemblance to a 

 bird's dropping on a leaf is carried out with extraordi- 

 nary detail. Such excreta consist of a * central and 

 denser portion, of a pure white chalk-like colour, 

 streaked here and there with black, and surrounded 

 by a thin border of the dried up more fluid part, 

 which, as the leaf is rarely horizontal, often runs for 

 a little way towards the margin ' and there evaporates, 

 forming a rather thicker extremity. The margin is 

 represented by a film-like web, with a thickened part 

 to represent the fluid which has run to the edge or 

 apex of the leaf ; the central mass is represented by 

 the spider itself with white abdomen and black legs, 

 lying on its back in the middle of the web, and held 

 in position by the spines on its anterior legs which 

 are thrust under the film. 1 The whole combination of 

 habits, form, and colouring afford a wonderful example 

 of what natural selection can accomplish. In such a 

 case there is no necessity for calling in the aid of any 

 other principle, for the addition of each new feature 

 and the improvement of every detail would at once 



1 H. 0. Forbes : A Naturalist's Wanderings in the Eastern Archi- 

 pelago, pp. 63-65. 



