4O Studies in the Theory of Descent. 



the wings (Fig. 15, Plate I.). This type, Bryonice, 

 occurs in Polar regions as the only form of Napi, 

 and is also found in the higher Alps, where it flies 

 in secluded meadows as the only form, but in other 

 localities, less isolated, mixed with the ordinary 

 form of the species. In both regions Bryonitz 

 produces but one generation in the year, and must 

 thus, according to my theory, be regarded as the 

 parent-form of Pieris Napi. 



If this hypothesis is correct if the variety 

 Bryonicz is really the original form preserved from 

 the glacial period in certain regions of the earth, 

 whilst Napi in its winter form is the first secondary 

 form gradually produced through a warm climate, 

 then it would be impossible ever to breed the 

 ordinary form Napi from pupae of Bryonicz by 

 the action of warmth, since the form of the species 

 now predominant must have come into existence 

 only by a cumulative action exerted on numerous 

 generations, and not per saltiim. 



The experiment was made in the following 

 manner : In the first part of June I caught a 

 female of Bryonite in a secluded Alpine valley, 

 and placed her in a capacious breeding- cage, where 

 she flew about among the flowers, and laid more 

 than a hundred eggs on the ordinary cabbage. 

 Although the caterpillars in the free state feed upon 

 another plant unknown to me, they readily ate the 

 cabbage, grew rapidly, and pupated at the end of 

 July. I then brought the pupae into a hothouse in 



