Adjustment of colour in various pupss, etc. 373 



faggot-stack, and Lad a roof of black net. Division (2) 

 had the same number of peeled and therefore nearly 

 white willow slips of the same size, and had a roof of 

 Avhite muslin. The sticks were secured by driving them 

 into the earth, and the cylinders were in both cases 

 exposed to the same amount of light, i. e. close to a 

 rather large window, but on most days moved from the 

 W.N.W. to the E.S.E. side of the house, and back, to avoid 

 hot sunshine. As larvse, where crowded, have been found 

 to affect ea(h other's pupal colouring (Phil. Trans. 1887, 

 /. c. Ent. Trans. 1892, /. c), only two or three were placed 

 in each cylinder. 



I exhibit the eleven pupae or pupa-cases, which were 

 obtained under these conditions. As the dark pigment 

 resides in the pupa-case, it is easy to see on examining 

 this whether the pupa was a green one or not, as, if the 

 pupa was a green one, the pupa-case is practically free 

 from pigment, though sometimes stained in places by the 

 meconium, whereas if the pupa was bone-coloured the case 

 is much darkened by brown or black markings. 



It was obviously desirable to ascertain what was the 

 proportion of grey * and yellow-green pupse in my stock, and 

 on j:roincr throucrli the whole remainder of them, 145 in 

 number, I found that 76 might be described as of the 

 ibrmer and 69 of the latter or yellow-green form. Many 

 of these however were of intermediate colouring, and 

 it was not easy to classify them. Seven of the 145 had 

 pupated on the green carrot- tops on which the larva had 

 been fed ; of these six were yellovj-green, one was grey. 



This made a very strong case for susceptibility, but it 

 was not conclusive, and I determined to try the experiment 

 on a larger scale with the second brood. 



Before describing in detail the results of this and other 

 experiments it is necessary to tabulate the colours which 

 the pupa of P. machaon is known to assume, so as to 

 have a standard of comparison. The following table and 

 description were made by Prof Poulton on May 2nd, 1899, 

 after carefully comparing the whole of my pupse together 

 with a number beloncjinsf to Mr. C. V. A. Peel. 



2. Results of the above Experiments. (E. B. P.) 



There is a distinct dimorphism in the pupas of Fapilio 



machaon, and the intermediate forms are very rare as 



* See note on page 374. 



