210 Mr. W. Bateson ow Variation in the 



tion of the food, and that it is prohahly a chlorophyll- 

 derivative ; (3), that it is imparted to the silk from the 

 mouth of the larva, and perhaps hy evacuation from the 

 intestine also. 



I have to thank Dr. A. Sheridan Lea for kindly ad- 

 vising me in the examination of this substance. 



II. The colours ofpupts o/ Vanessa urticae. 



The pupae of V. urticxe and of some other butterflies 

 are known to be sometimes much pigmented, and some- 

 times very light, with little or no pigment. Apart from 

 the pigmentation, they also vary greatly in the extent 

 and brightness of the metallic lustre, which is so marked 

 a feature of these forms. Poulton* has described experi- 

 ments showing that there is a relation between these 

 variations and the colours of the linings of the cages in 

 which the larvae pupated. In the past summer I made 

 experiments of the same kind on V. urticre, and the 

 results fully bore out Poulton's account, to which I can 

 add little. 



The larvae were collected when about half-grown, and 

 were put into shallow cardboard boxes, through one end 

 of which the stem of a nettle was passed. The boxes 

 were lined with one or other of the following papers : — 

 (1) gilt, (2) silver, (3) yellow, (4) white, (5) black, or (6) 

 painted with Indian ink. The face of each box was 

 covered with a pane of glass, and the boxes were all 

 placed upright in a row facing a south window. During 

 the three weeks through which the experiments con- 

 tinued there was generally a bright sun, so that the 

 boxes became very hot. In some of them there was a 

 good ventilation maintained, while others were kept very 

 close, so that by the transpiration from the plant the 

 atmosphere of the box was saturated with moisture, 

 which also trickled continually down the glass. I did 

 not find that the condition of moisture or dryness 

 affected the colours of the pupae. It is perhaps un- 

 necessary that these experiments should be described in 

 detail, as Poulton's description is complete. 



One series of experiments, made by way of control, 

 have, however, some interest, as materially confirming 

 the view that the change in the colours is really due to 



* E. B. Poulton, Phil. Trans., 1887, vol. clxxviii., B, p. 311. 



