On the Seasonal Dimorphism of Butterflies. 5 1 



forms. The form B thus occurs in both climates, 

 appearing as the summer form in Germany and 

 as the winter form in Italy. The German winter 

 variety A, is entirely absent in Italy (as I know 

 from numerous specimens which I have caught), 

 whilst the Italian summer form, on the other hand, 

 (var. Allous, Gerh.), does not occur in Germany. 

 The distinctions between the three forms are 

 sufficiently striking. The form A (Fig. 18, Plate 

 II.) is blackish brown on the upper side, and has 

 in the most strongly marked specimens only a trace 

 of narrow red spots round the borders ; whilst the 

 form B (Fig. 19, Plate II.) is ornamented with vivid 

 red border spots ; and C (Fig. 20, Plate II.) is dis- 

 tinguished from B by the strong yellowish-brown 

 of the under side. If we had before us only the 

 German winter and the Italian summer forms, we 

 should, without doubt, regard them as climatic 

 varieties ; but they are connected by the form B, 

 interpolated in the course of the development of 

 both, and the two extremes thus maintain the 

 character of mere seasonal forms. 



E 2 



