206 THE ENTOMOLOGIST. 



will have to be rejected by degrees. These specimens, however, 

 are just those which still contain levana-detevmma.nis, and in 

 which both of the characters are mixed. In this case, therefore, 

 the levanaiovm. must wholly disappear, and both broods become 

 similar. 



Only if the levana colouring were more advantageous in the 

 spring than the prorsa colouring, it could and must remain, and, 

 indeed, from the fact that only a part of the id contained in the 

 germ-plasm was altered, while another part remained unaltered. 

 There cannot well be any doubt but that levana is the original 

 form, as, according to Trybom's observations, it is at the present 

 time the only form in those places where only one brood occurs 

 in the year, as in Siberia on the Yenesei. 



But if it is not at present possible to bring forward a proof 

 that the upper sides of prorsa and levana are to be regarded as 

 protective colouring, yet the delicate combination and generally 

 the kind of variability of both patterns of colour are decisively 

 against their interpretation as direct climatic forms. 



Already, in my work on seasonal dimorphism of the year 

 1875,* I laid stress upon the fact, that the ^9rorsa-form could in 

 no way be simply referred to an increase of the black. I there 

 said (page 40) : — '' Even in the case of species the summer form 

 of which really possesses far more black than the winter form, 

 as, for instance, Vanessa levana, one type cannot be derived from 

 the other simply by the expansion of the black spots present, 

 since on the same place where in levana a black band runs" 

 (across the hind wings), '^ prorsa, which otherwise possesses much 

 more black, has a white line. The intermediate forms which 

 have been artificially produced by the action of cold on the 

 summer generation present a graduated series, according as 

 reversion is more or less complete ; a black spot first appearing 

 in the middle of the white band of prorsa, and then becoming 

 enlarged until, finally, in the perfect levana, it unites with 

 another black triangle proceeding from the front of the band, 

 and thus becomes fused into a black bar. The white band of 

 prorsa and the black band of levana by no means correspond in 

 position ; in prorsa quite a new pattern appears, which does 

 not originate by a simple colour replacement of the levana 

 markings." 



This is perfectly accurate, although later on a fanatic oppo- 

 nent of the evolutionary doctrine simply described it as '* false," 

 and as a "want of observation." t The different stages of the 

 conversion of the levana- into the prorsa-maicWng can be followed 

 to some extent in the different forms of porima, and it is certainly 



•-;: "Weismann, " Studien zur Descendenztheorie. I. Ueber den Saison 

 Dimorphismus der Schmetterlinge." Leipzig, 1875. 



f Johannes Scliilde, " Gegen pseudodoxische Tiansmutationslehren, ein 

 Entomolog." Leipzig, 1879. 



