SEASONAL DIMORPHISM OF LEPlDOPTERA. 247 



only happen if the white form had existed before the dark one, 

 and if "white" ids, therefore, were usually still latent in the 

 germ-plasm of hryonice As, however, in the new experiments 

 with hnjon'ice here described there were isolated white specimens, 

 a final decision must be suspended until further experiments 

 have been made, as is stated above in the ''results" of the 

 experiments. Seitz is inclined to regard the napi-ioim as the 

 primary one, since most of the species of Pkris are white ; but 

 it might be argued against this that the dark bryonies occurs in 

 widely removed regions of the earth, — in the Alps, the Jura, and 

 the Polar Kegions, — a range which points to a common circum- 

 polar origin and subsequent separation after the close of the 

 glacial epoch. Against this argument, indeed, the view might 

 be held, that the black of the female hryonice is an adaptation to 

 a cold climate, in the sense of Lord Walsingham, which had been 

 formed by selection independently in the Alps and in the far 

 north. We do not get much further with the decision of the 

 particular question, but perhaps from its profitable discussion 

 we see afresh, how little we know of the biology of insects, and 

 how difficult it is to obtain a true solution of particular questions. 

 Now if, as I think is unavoidable, direct seasonal dimorphism 

 is distinguished from adaptive, the question is, which of the 

 known cases belongs to the one, and which to the other category. 

 But in order to decide this, more accurate researches especially 

 directed to this point are necessary, as they are not yet available. 

 In cases in which double marking and colouring occur, which are 

 evidently protective, as in the tropical Satyridae bred by de Nice- 

 ville and Junonia almana-asterie described by Seitz as seasonally 

 dimorphic, seasonal dimorphism can with greater safety be 

 referred in anticipation to the processes of selection. x\ppa- 

 rently Grapta inter rogationis also, with its two seasonal forms 

 YHY.fahricii and var. umbrosa, investigated by W. H. Edwards, 

 is to be referred to double protective adaptation, since in this 

 case the protective under side exhibits great differences. But, 

 on the one hand, considerable differences are present on the 

 upper side ; and on the other, it is yet to be proved in what way 

 the protective under side of the summer form is a better pro- 

 tection during the summer time, than the under side of the 

 autumn and spring forms, and vice versa. The under side of the 

 species of Grapta is always to a high degree protective, but it is 

 very different in the different species, and with many of them 

 also appears to alter according to the time of year. I often 

 thought that I had found a seasonal dimorphism of the under 

 side in our Grap)ta c-album, but the matter has not been followed 

 up sufficiently closely to enable us to exclude other explanations 

 of the variability observed, especially individual and local diffe- 

 rences. I consider it, however, very possible that an adaptive 

 seasonal dimorphism of the under side will yet be found. A. Seitz 



