VIII ORIGIX AXD USES OF COLOUR IX ANIMALS 197 



This Avas sho^vn by feeding two sets of larvae on the same 

 plant but exposed to differently coloured siuToundings, 

 obtained by se^Wng 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 larvae, confirming the 

 experiments on different individuals of the same batch of 

 l2LTVi<e which had been supj^lied with different food-plants or 

 exposed to a different coloured light. 



An even more interesting series of experiments was made 

 on the colours of pupae, which in many cases were known tc 

 be affected by the material on which they underwent their 

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

 that the pupae of the common cabbage butterflies (Pieri.s 

 brassicaB and P. rapae) were either light, or dark, or gTeen, ac 

 cording to the coloured boxes they were kept in, or the colour. . 

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

 Mrs. Barber in South Africa found that the pupie of Papilio 

 Nireus underwent a similar change, being deep green when 

 attached to orange leaves of the same tint, pale yello^^^sh-gTeen 

 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 larvae of 

 several of our common butterflies were the means of clearing 

 up several imj^ortant points. He showed that the action 

 of the coloured light did not affect the j^upa 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. When 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 siUTounding coloiured 

 surfaces determines, to a considerable extent, the colour of 

 the pupa. By the application of various surrounding 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 rapse 



