112 THE COLOURS OF ANIMALS 



(Uropteryx sambucata) becomes light-coloured when 

 the caterpillar has been placed upon white paper 

 shortly before pupation (see fig. 23). The chrysalis 

 is usually dark (see fig. 24), and is contained in a 

 cocoon which is formed of the brown fragments of 

 leaves or twigs spun together with threads of silk. 

 The cocoon, which is suspended from the food-plant 

 and swings freely, is so loose and open in texture that 

 the enclosed pupa is easily seen, and is in fact as 

 exposed as that of many butterflies. 



The chrysalides of butterflies are generally freely 

 exposed, and many species have been proved to possess 

 the power of adjusting the pupal colour to that of 

 the adjacent surface. Such pupae are often suspended 

 head downwards from a boss of silk, to which the 

 hooks at the posterior end are affixed ; or they are fre- 

 quently attached horizontally, or in a vertical position 

 with the head upwards, by similar posterior hooks and 

 a strong silken girdle, which is fixed on either side to 

 the supporting surface, and which sinks into a groove 

 across the back of the pupa. The group which in- 

 cludes the Tortoiseshell and Peacock Butterflies adopts 

 the former mode of suspension; that to which the 

 * Garden Whites ' belong adopts the latter. 



