VII r ORIGIN AXD USES OF COLOUR IX ANi:\IALS 197 



This was sho"nTi by feeding two sets of larvne on the same 

 plant but exposed to differently coloured surroundings, 

 oljt;dned by se^^ang the leaves together, so that in one case 

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

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

 corresponding change of colour in the larvre, confirming the 

 experiments on different indiAiduals of the same batch of 

 larva3 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 pu})a% which in many cases were known to 

 be affected by the material on Avhich they underwent their 

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

 that the pupa3 of the common cabbage butterflies (Pieris 

 brassica3 and P. rapre) Avere either light, or dark, or green, ac- 

 cording to the coloured boxes they Avere kept in, or the colours 

 of the fences, Avails, etc., against AAdiich they Avere suspended. 

 Mrs. Barber in South Africa found that the pup^ of Papilio 

 Nireus underAA^ent a similar change, being deep green Avhen 

 attached to orange leaA^es of the same tint, pale yelloAAnsh-green 

 Avhen on a branch of the bottle-brush tree Avhose half-dried 

 leaves Avere of this colour, and yelloAvish Avhen attached to 

 the AA'Ooden frame of a box. A feAv other obserA^ers noted 

 similar phenomena, but nothing more Avas done till Mr. 

 Poulton's elaborate series of experiments AAdth the larvse of 

 several of our common butterflies Avere the means of cleariner 

 up several important points. He shoAved that the action 

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

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

 a caterpillar has done feeding it AA^anders about seeking a 

 suitalile place to undergo its transformation. When this is 

 found it rests quietly for a day or tAvo, spinning the Aveb from 

 Avhich it is to suspend itself ; and it is during this period of 

 quiescence, and perhaps also the first hour or tAA-o after its 

 suspension, that the action of the surrounding coloiu-ed 

 surfaces determines, to a considerable extent, the colour of 

 the pupa. By the application of A'arious surrounding colours 

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

 of the pupa of the common tortoise-shell butterfly from neai'ly 

 l)lack to ])ale, or to a brilliant golden ; and that of Pieris rapse 



