icmperafure on the colouring of Lcjndojitera. 41 



applied, and which are now in progress ; but the evidence 

 is so strong that I do not like to delay calling attention 

 to the point, with a view of, if possible, enlisting other 

 observers, until the question shall have been decided by 

 exact measurements. I think it is generally assumed 

 that, once the pupal state is entered upon, the size and 

 shape of the imago are fixed once for all (except where the 

 wings afterwards expand imperfectly), and no doubt that 

 is true to the extent that, in an insect of variable size, 

 the size the larva attains is the chief factor in the size 

 of the imago, and under ordinary circumstances the only 

 one. But there is very strong evidence that the size 

 may be affected by the circumstances surrounding the 

 pupa. The impression that this is so can hardly fail to 

 be gathered by any one who sees the long series I possess 

 of insects differently treated in the pupal stage, and I 

 think I may say that this is the impression actually pro- 

 duced on all my friends who have seen these long series. 

 It is an effect which by no means appears to operate in 

 the same direction in all species. 



In the three Selenias, of both the spring and the sum- 

 mer emergences, those at 80° appear smaller than those 

 kept at and under 60°; it seems to be the same in 

 falcatai'ia, as well as in B. quercus and its var. callunce. 

 In F. urtica there appears little difference, if any, in the 

 size of butterflies from pupae at 80° and from pupae at 

 about 60° ; but those from the pupae kept at 47° are 

 generally smaller. I may add that on consulting the 

 record of experiments on P. j)haros, as recorded in 

 * Weissmann's Studies in the Theory of Descent,' by 

 Meldola, I find it stated that the butterflies from three 

 pupae which had been iced were sensibly smaller than 

 the rest. 



As to sluqje, I can only say at present that I think this 

 is affected by temperature. I think that in the Selenias 

 of which the pupae were kept at the lower temperature, 

 the fore wings are longer and more angular; but on this 

 subject I am making some exact observations, and in the 

 meantime venture to ask the attention to it of those who 

 have the opportunity of investigation. 



The general differences in size, and possibly in shape, 

 are, I think, exemplified by the specimens I exhibit, 

 which were selected solely for colour and markings. 



Species not found to be affected by temperature. — It may 



