Adjustment of colour in various impiB, etc. 421 



otherwise similarly fixed, one was a greenish (1 y) and 

 one, emerging, was probably a (1 y) or (2). 



Two pupffi were fixed to the parti-coloured surface of 

 the roof. Of these one diagonally crossed two black 

 s([uares in a manner very similar to that of the first 

 described of the two dead pupae in the first box, which 

 could not be classified with certainty. The direction of 

 the body was oblique with the head away from the light. 

 It had emerged, but had clearly been a (2) or (3). The 

 second was fixed in another bay, near to and parallel with 

 the glass. The posterior § of the body crossed a black 

 square, the anterior ^ was on the next orange one. It had 

 emerged but had evidently been a (1 ;i3) with quite dark 

 pigmentation, Tiiere was no trace of less pigmentation in 

 the anterior third of its body. 



These results entirely confirm those obtained in the 

 first box. 



Although further experiments of this kind are to be 

 desired, especially upon so sensitive a species as P. napi, 

 it may be regarded as certain that the conclusions derived 

 from the earlier experiments with conflicting colours are 

 sound, and that not parti-coloured pupce but uniform 

 intermediate ones are obtained in this way. 



i^.— NOTES ON THE STRUGGLE FOR EXISTENCE 

 IN THE LARViE OF Fieris brassier. (E.B.P.) 



I have previously noted the numbers of this species 

 which perish from the attacks of parasites in a year in 

 which the larvae are specially abundant. It seemed of 

 interest to obtain further records, and I accordingly asked 

 Mr. Holland and Mr. Hamm to keep notes of tiie number 

 of larvae attacked by ichneumons and the numbers dying 

 apparently from other causes, which they removed from 

 the cases containing the mixed larvae from St. Helens and 

 Oxford (see p. 409). The results are recorded in the table 

 on the following page. 



In the breeding-cases from which these larvae were 

 removed only 121 pupae were taken, including the dead 

 ones; so that the extinction is on a vast scale. Even if 

 it be conceded that the larvae dying without the appear- 

 ance of parasites, and the dead pupae, were entirely due to 

 the conditions of experiment (such as the possible intro- 

 duction and spread of some form of bacterial disease), the 



