1 6 Studies in the Theory of Descent. 



then emerged in the perfect winter form, Levana. 

 Such a result, taken in connexion with the cor- 

 responding experiment upon Pieris Napi, would 

 warrant the conclusion that the direct action of a 

 certain amount of cold (or of retardation of deve- 

 lopment) is able to compel all pupae, from which- 

 ever generation derived, to assume the winter 

 form of the species. From this the converse 

 would necessarily follow, viz. that a certain amount 

 of warmth would lead to the production of the 

 summer form, Prorsa, it being immaterial from 

 which brood the pupae thus exposed to warmth 

 might be derived. But the latter conclusion was 

 proved experimentally to be incorrect, and thus 

 the former falls with it, whether the imagined ex- 

 periment with Prorsa had succeeded or not. 



I have repeatedly attempted by the application 

 of warmth to change the winter into the summer 

 form, but always with the same negative result. 

 It is not possible to compel the winter brood to 

 assume the form of the summer generation. 



A. Levaua may produce not only two but three 

 broods in the year, and may, therefore, be said to 

 be polygoneutic One winter brood alternates 

 with two summer broods, the first of which appears 

 in July, and the second in August. The latter 



14 It seems to me very necessary to have a word expressing 

 whether a species produces one, two, or more generations in 

 the year, and I have therefore coined the expression mono-, di-, 

 and polygoneutic from yovevw, I produce. 



