( xlvi ) 



undergo the change to the pupal state. Mr. Trimen said he was 

 able to confirm this statement. 



The Rev. W. W. Fowler exhibited a number of minute Acari, 

 which had been doing injury to fruit trees near Lincoln. 



Mr. E. B. Poulton gave an account of the experiments recently 

 made by him, with the object of ascertaining the cause of the 

 relation of pupal colour to that of the surface on which the larval 

 skin is thrown off, and also exhibited a frame he had devised for 

 making these experiments. He stated that he had repeated Mr. 

 T. W. Wood's experiments, communicated to the Society a few 

 years ago, and had quite confirmed the accuracy of his results. 

 The experiments were extended to the Vane8sid(B, and it was 

 found that the metallic colour, which is common on these pupae, 

 could be controlled by the choice of appropriate surroundings for 

 the larva before pupation — a gilt surface producing the metallic 

 appearance in the great majority of pupse employed, to an extent 

 which is rarely seen under other conditions ; while a black surface, 

 on the other hand, produces very dark pupse, with the slightest 

 trace (if any) of the gilded appearance. In order to investigate the 

 subject further, and to find out the organ which was affected by the 

 surroundings, and caused the appropriate appearance in the pupa, 

 it was necessary to first ascertain the exact period during which 

 the influence exerted itself. Mr. T. W. Wood had assumed that 

 the change was caused immediately after the larval skin was thrown 

 off, the moist freshly-exposed pupal skin being supposed to be 

 photographically sensitive to surrounding colours. Mr. Poulton, 

 however, took the view that the cause works on the larva before 

 pupation, as this agreed with the results of a very similar 

 investigation upon the changes of colour in larvse, upon which 

 he had been engaged for some years. Further, Mr. Wood's 

 theory was unsupported by any proof, and did not explain such 

 an obvious objection as the position of pupsB which throw off the 

 larval skin on a dark night. Mr. Poulton therefore investigated 

 the period which intervenes between the cessation of feeding and 

 pupation in the larvse of the common Vanessa (F. urtica), and 

 found that the influence works during a considerable period, of 

 very many hours, before the final change, — long enough to include 

 many hours of daylight in all cases. The subject was inves- 

 tigated by choosing two conditions which produced the most 

 opposite results (black and gilt or black and white surroundings), 



