On the Seasonal Dimorphism of Butterflies. 9 



tinued many disappearing entirely without my 

 being able to find their remains until after the 

 ninth day, when they had all, with one exception, 

 been slain by their nocturnal foes probably 

 spiders and Opilionidce. 



Diurnal Lepidoptera in a position of rest are 

 especially exposed to hostile attacks. In this 

 position, as is well known, their wings are closed 

 upright, and it is evident that the adaptational 

 colours on the under side are displayed, as is most 

 clearly shown by many of our native species. 9 



Now, the differences in the most pronounced 

 cases of seasonal dimorphism for example, in 

 Araschnia Levand are much less manifest on the 

 under than on the upper side of the wing. The 

 explanation by adaptation is therefore untenable ; 

 but I will not here pause to confute this view more 

 completely, as I believe I shall be able to show 

 the true cause of the phenomenon. 



If seasonal dimorphism does not arise from the 

 indirect influence of varying seasons of the year, 

 it may result from the direct influence of the 

 varying external conditions of life, which are, 

 without doubt, different in the winter from those 

 of the summer brood. 



There are two prominent factors from which 

 such an influence may be expected temperature 



9 [The fact that moths which, like the Geometrae, rest by 

 day with the wings spread out, are protectively marked on the 

 upper side, fully corroborates this statement. R.M.] 



