89 



goneutic species, and that its digoneutism has been acquired, 

 as the climate of the palaearctic region became more genial 

 after the glacial period. It appears to me, therefore, that 

 the effect of the cold on the pupa has prevented the insect 

 from attaining to its highest imaginal development both in 

 the colour and pattern of the wings. 



It should I think be borne in mind that larvae in the spring 

 and summer months have the advantage of feeding on de- 

 veloping and fresh leaves ; but, on the contrary, in the autumn 

 their food becomes daily less succulent and probably more 

 innutritions. It, therefore, might be expected from a priori 

 considerations that those larvae of a digoneutic species which 

 fed on the richest food would develop into the finest and 

 most brilliantly coloured imagines. 



I anticipated that there would this year have been an in- 

 crease in the size of the butterflies, as a result of the remarkably 

 long hot summer, as the season progressed, such being the 

 case in Japan, where a longer and warmer summer than ours 

 obtains. Mr. Pryer, in his work " Rhopalocera Nihonica," 

 writes thus of Papilio niachaon : " The first imago appears 

 in March, from larvas which have fed up late in the preceding 

 autumn. These March specimens are invariably small and 

 light coloured, and are the machaon form ; as the summer 

 advances the- successive broods increase in size and depth of 

 coloration, until August, when the hippocrates form appears." 

 In the illustrations given in the work of the two emergences, 

 the spring measures 8o mm., and the August 130 mm., in 

 expanse of wings. 



But my expectations have in no way been realized, the 

 broods of the digoneutic and polygoneutic butterflies have 

 shown no marked increase in size ; Heodes phloeas and Pieris 

 rapCB, which have produced several broods, have remained of 

 the normal size ; and monogoneutic species have in this 

 respect been unaffected ; indeed, with regard to Argynnis 

 paphia and the dimorphic female valesina, a very dwarf race 

 has been common in the New Forest, flying at the same 

 time as those of the normal size. In some species both of 

 butterflies and moths the imagines of the second emergence 

 have been smaller than usual. 



The study of variation in British Lepidoptera has given 

 new life to the collection of indigenous species of that order, 

 and many singular facts have been brought to light ; extreme 

 aberrations, such as it seemed improbable would occur again, 

 have been found in districts most remote from these Islands. 



I have on a previous occasion brought before the Society 



