28 THE ENTOMOLOGIST. 



and darker than the summer brood, a condition which has been 

 attributed to the effects of cold while in the pupa stage. But, 

 strangely enough, a moderate amount of cold appears to have an 

 opposite effect, for in our climate the spring Pieridse, which are 

 dark in America, are distinctly lighter than the summer forms, 

 and the imported P. rapa would seem to have retained that 

 character somewhat in America. Also, as regards size, I believe 

 that it is found that the races of large silk-moths, which are bred 

 on the cooler slopes of the Himalayas, are invariably larger and 

 finer than those of the same species from the heated plains of 

 India; and this has been attributed to their longer sojourn in 

 the pupal state, whereby they have more time for development. 

 The only theory I can advance to harmonise these various facts 

 may seem to many a somewhat unwarranted one, and I shall look 

 with interest for any comments on it. The darker and smaller 

 forms may be supposed always to be those whose development 

 has been quick, the metabolism great in proportion to the 

 growth, while the larger and lighter forms have developed more 

 slowly, with a longer period of growth, and less intense 

 metabolism ; in short, as Mr. P. Geddes would say, the first have 

 developed katabolically, the last anabolically. When eggs or 

 seeds are subjected to a low temperature, although life is not 

 necessarily extinguished, growth and metabolism cease. The 

 winter in North America is sufficiently cold to have a like effect 

 upon hybernating pupee, — they live, but do not grow. The 

 summer comes on with comparative suddenness, and the hot 

 rays of the sun throw them into the most intense metabolism, 

 so that the imago emerges with the wing-structures, so far from 

 having developed slowly and in the cold, presenting every 

 evidence of rapid change. In a climate like that of England, 

 however, the winter is not cold enough to entirely arrest wing- 

 growth, and hence the spring emergences present usually some 

 evidence of slow change accompanied by gradual growth. It will 

 probably be objected to the above theory, that summer in 

 America is at least as hot as spring, so why do not the summer 

 forms present at least as much evidence of quick change ? To 

 which I can only reply, that I am inclined to suppose that the 

 vital structures and organs of generation develop at a much 

 lower temperature than the wings, of which theory confirmation 

 will be seen in such examples as the normally wingless, but 

 otherwise perfect, Choreius ineptus, which is said often to develop 

 wings in unusually hot seasons. I hold, therefore, that the North 

 American species hybernating in the pupal state attain a nearly 

 perfect development of their vital functions before the spring, 

 although wing-growth has been in abeyance ; but those pupating 

 and emerging in the summer cannot assume the perfect state 

 until the time necessary for the growth of the vital and repro- 



