viii ORIGIN AND USES OF COLOUR IX AXDIALS 197 



This was shown by feeding two sets of larvae on the same 

 plant but exposed to differently coloured surroundings, 

 obtained by sewing the leaves together, so that in one case 

 only the dark upper surface, in the other the whitish under 

 surface was exposed to view. The result in each case was a 

 corresponding change of colour in the larva?, confirming the 

 experiments on different individuals of the same batch of 

 larva? which had been supplied with different food-plants or 

 exposed to a different coloured light. 



An even more interesting series of experiments was made 

 on the colours of pupa?, which in many cases were known to 

 be affected by the material on which they underwent their 

 transformations. The late Mr. T. W. "Wood proved, in 1867, 

 that the pupa? of the common cabbage butterflies (Pieris 

 brassica? and P. rapa?) were either light, or dark, or green, ac- 

 cording to the coloured boxes they were kept in, or the coloius 

 of the fences, walls, etc., against which they were suspended. 

 Mrs. Barber in South Africa found that the pupa? of Papilio 

 Nireus underwent a similar change, being deep green when 

 attached to orange leaves of the same tint, pale yellowish-green 

 when on a branch of the bottle-brush tree whose half-dried 

 leaves were of this colour, and yellowish when attached to 

 the wooden frame of a box. A few other observers noted 

 similar phenomena, but nothing more was done till Mr. 

 Poulton's elaborate series of experiments with the larva? of 

 several of our common butterflies were the means of clearing 

 up several important points. He showed that the action 

 of the coloured light did not affect the pupa itself but the 

 larva, and that only for a limited period of time. After 

 a caterpillar has done feeding it wanders about seeking a 

 suitable place to undergo its transformation. AYhen this is 

 found it rests quietly for a day or two, spinning the web from 

 which it is to suspend itself : and it is during this period of 

 quiescence, and perhaps also the first hour or two after its 

 suspension, that the action of the siuroiinding coloured 

 surfaces determines, to a considerable extent, the colour of 

 the pupa. By the application of various sirrroimding colours 

 during this period, Mr. Poulton was able to modify the colour 

 of the pupa of the common tortoise-shell butterfly from nearly 

 black to pale, or to a brilliant golden ; and that of Pieris rapa? 



