PROTECTIVE RESEMBLANCE 137 



in almost all eases of special protective resemblance, 

 we find that the most effective pose — i.e. that calculated 

 to enhance to the full the concealing value of the insect's 

 coloration — is the one which is habitually adopted. Of 

 course this does not justify the assumption that insects 

 have any knowledge of their appearance, or that they 

 consciously take up appropriate attitudes : but it does 

 lead us to conclude that the same principle of natural 

 selection which has fashioned an insect's structure, has 

 also modified its habit so that the one may accord with 

 the other. The stick-like form of a caterpillar would be 

 of little service if the creature lacked the instinct to pose 

 in a stick-like manner. 



This correlation of structure and instinct constitutes 

 a wide field for investigation. It is not enough merely to 

 know what a creature does ; we want to find out also 

 the reason for its actions — the bearing which they have 

 upon the exigencies of its life. For instance, many 

 butterflies — such as the grayling {Satyi'us semele) — which 

 rest upon the ground, have the habit of dropping suddenly 

 after a short flight, and lying over on one side. This 

 trick not only serves to throw the protective colouring of 

 their wings into greater prominence, but also to minimise 

 — it may be completely to cover — the shadow which 

 the insect casts. The habits of an African butterfly 

 (Hamanumida dcedalus) are said to vary in different 

 districts. In West Africa it rests with its wings folded 

 above the back after the common manner of butterflies, 

 in which position the tawny underside, which agrees with 

 the general tone of the soil, is exposed to view. In South 

 Africa, however, the same insect sits with its wings fully 

 expanded, showing the white-spotted upper surface 

 which resembles the colours of the rocks in that region. 

 There is also much evidence to support the theory that 



