the colours of certain Lepicloptera. 341 



during the course of the experiment. But the results in 

 reality harmonise with those given above, for the dark 

 larVfie were never like those of I., but tended more in the 

 direction of the mouldy, dark grey, or blackish appear- 

 ance of the twigs or leaves. Sometimes, however, the 

 larvae were evidently affected to the end by the earlier 

 appearance of their environment. 



Some conclusions as to the period of greatest suscepti- 

 bility may also be drawn from these results. The facts 

 that the single exception in I. was older than the other 

 larvfe, — that the larvfe transferred from II. to XXVII. for 

 nearly the whole of the two last stages could change so 

 little, — that the larvfe of IV. were considerably darker 

 than III., in which the environment changed more slowly, 

 — and that the earlier colour of the surroundings pro- 

 duced its full effect long after its change, in certain ma- 

 ture larvfe of III., IV., and VII., — clearly indicate that 

 the time of chief susceptibility has been passed when the 

 last stage but one has been reached. It is equally clear, 

 however, that there is some susceptibility in certain 

 larvfe during the last two stages. On the other hand, the 

 condition of the larv?e during the earliest period of growth 

 does not seem to produce any effect, or at any rate does 

 not interfere in the least with the full power of the sur- 

 roundings which are subsequently applied. Thus the 

 larvae of these experiments began to hatch on .Tune 29th, 

 and were kept in green surroundings until July 9th or 

 10th, when the dark environments were substituted. 

 But the earlier green surroundings probably did not 

 diminish the influence of the later environment in any 

 instance, except perhaps the single green larva in I. 

 The same conclusions are to be gained by a study of 

 nearly all the species experimented with, for the en- 

 vironments were very rarely applied immediately after 

 hatching. 



And this is what we should expect from the habits of 

 the larva3, which always rest on the leaves during the 

 earliest stages. It is probable that the colours of the 

 mature larvae are decided when they abandon this habit, 

 and first come to rest on the twigs. Too early suscepti- 

 bility would render all larvae green. 



"We may therefore conclude that the time of effective 

 susceptibility lies somewhere within the second and third 

 stages of larval life, and perhaps in the third rather than 

 the second. 



