4-28 Mr. F. Merrifield and Mr. E. B. Poulton on 



/.—EXPERIMENTS AND OBSERVATIONS UPON 

 THE SUSCEPTIBILITY OF CERTAIN LEPI- 

 DOPTEROUS LARV^ AND PUP^ TO THE 

 COLOURS OF THEIR SURROUNDINGS. (A. 

 H. Hamm and E. B. P.) 



1. Stauropus fagi. Mr. W. Holland and Mr. A. H. 

 Hamm of the Hope Department, who are extremely 

 skilled and accurate observers, drew my attention last year 

 (1898) to the fact that the larva; of this species differ in 

 tint according as they are reared upon beech or birch, and 

 that the colours are in each case such as to conceal them. 



During the present year Mr. Hamm reared two 

 batches (from difierent parents) upon the same food-plant, 

 beech, but in other respects under very different conditions 

 fis regards environment. One of the batches was reared 

 in a white tissue-paper lined rectangular glass case with a 

 perforated zinc lid, the other in a similar case lined with 

 black tissue-paper. We compared the two, placing both 

 batches on white paper, on July 13, 1899. 



There were 24 larvas in the batch reared in the white 

 case, and of these all but 2 were in the last stage and 

 mostly advanced in it. All but 1 were 7nuch lighter than 

 larva? of this species usually met with in nature, and 

 some most markedly lighter. The other batch consisted of 

 14 larvae, of which 10 were in the last stage (mostly 

 advanced), 1 in the la.st but one, and 3 in the last but 

 two. All were very dark, and most of them far darker 

 than those generally met with in nature. It is clear that 

 this species is highly sensitive, and it would be of great 

 interest to repeat the experiments under conditions which 

 have been found in other larvae to produce the strongest 

 effects. It is remarkable that such considerable results 

 followed from surroundings which were not apparently in 

 contact with the larvae (for these at any rate when they 

 were examined rested upon the twigs and not upon the 

 walls of the case). I do not think, in any of the previous 

 experiments with larva?, that equal effects have been 

 produced in this manner ; and one is tempted to enquire 

 whether it is possible that the larva? in earlier and 

 specially sensitive stages, did actually rest upon the black 

 and white walls of the cases. 



2. Notodonta ziczac. My friend Mr. Arthur Sidgwick 

 showed me, in the summer of last year (1898), a larva of 



