180 THE ENTOMOLOGIST. 



the pupal period, which directly formed the species in one way 

 or the other, and I felt the more justified in so doing, as the 

 climatic varieties form a parallel to the seasonal forms, and as 

 the former must without doubt be referred to the direct influence 

 of climate, especially of temperature. 



Thus, for example, Chrysophanus phloeas is seasonally dimor- 

 phic in Sardinia and at Naples ; the summer form, which 

 develops during the summer heat, is very dark, almost black, 

 but the spring form corresponds with our German red-golden 

 phloeas. 



Although to-day I still look upon this view as correct, and a 

 directly altering effect of temperature as proved, yet I have 

 gradually been convinced, that this is not the sole origin of 

 seasonally dimorphic variability, but that there is also adaptive 

 seasonal dimorphism. We must, I believe, distinguish direct and 

 adaptive seasonal dimorphism ; and I see in this distinction an 

 important advance, which before all places us in a position to 

 explain the results of the various experiments undertaken by 

 myself and others in a much more satisfactory manner. 



I have already pronounced this view in a lecture* delivered at 

 Oxford in the beginning of 1894, and I have sought to show that 

 adaptive seasonal dimorphism, which I had previously only put 

 forward as possible, does actually occur. The example there 

 given for perfect insects was, indeed, only a hypothetical one, 

 viz. the case of Vanessa prorsa-levana ; but for larv?e, at least, I 

 can select an example from Edwards's excellent work on the 

 North American butterflies with tolerable certainty, viz. that of 

 Lyccena p)seudargiolus, which will be more accurately discussed 

 later on. I did not then know, what I learnt shortly afterwards 

 from an interesting little pamphlet of Dr. G. Brandes, that cases 

 of seasonal dimorphism had been known for a long time among 

 tropical butterflies, and that among these, at least, one of the 

 seasonal forms depends upon the assumption of a special pro- 

 tective colouring. Brandes maintains, with justice, that the 

 view hitherto widely held among us is erroneous, according to 

 which seasonal dimorphism was not to be expected in tropical 

 countries, since the alternation of seasons is absent there. 

 Periods of rain and drought, at least for many tropical countries, 

 form such an alternation very sharply. At any rate, Doherty 

 and, somewhat later, de Niceville, have pointed out, for Indian 

 butterflies, a series of seasonally dimorphic species, not merely 

 by observation of the alternation of the two forms in nature, but 

 by rearing the one form from the eggs of the other ; thus among 

 Satyrids of the genera Yphthima, Mycalesis, and Melanitis, and 

 for the species of Jiuioiiia, it is accepted as proved ; and in all 

 these cases the difference between the two forms principally con- 



"'^' ' Aeussere Einfliisss als Entwicklungsreize,' Jena, 1894. 



