184 THE ENTOMOLOGIST. 



be stirred to activity in different ways, just as also Dr. Dixey 

 has interpreted — certainly with justice — many of Merrifield's 

 cold and heat aberrations as partial reversion to ancestral 

 characters. With Vanessa io, at least, a quite striking agree- 

 ment in the marking of the fore wings with Va^iessa urticce and 

 its nearest allies is brought about by the action of cold, which 

 does not admit of another explanation. Standfuss and E. 

 Fischer also reared an exactly similar aberration by the con- 

 tinued action of ice upon the pupae, and they also interpret it as 

 reversion in the direction of Vanessa urticce.* Moreover, it 

 seems to me important, that all these experimentalists had to 

 first subject the pupae, after the long cooling (on ice 8-42 days), 

 to a higher temperature for a longer time before they emerged. 

 With Merrifield it still required 18 days of a temperature of 

 16° C, with Standfuss 9-10 days at "the room temperature." 

 The chemical pi'ocesseSy therefore, of the formation of colour did not 

 go on here under the influence of cold, but of medium heat — 

 another sign, that it is here a question of the indirect effect 

 of cold. 



Thus it is also in all probability in the second land of seasonal 

 dimorphism— the adaptive. Two different patterns will be present 

 here close to one another as rudiments in the germ-plasm, and 

 the question as to which of the two kinds shall become active is 

 decided in the period immediately after pupation, not later. It 

 can scarcely be otherwise, as with this kind of seasonal dimor- 

 phism not merely the quality of the colour is concerned, but 

 also the whole pattern, — in many cases, indeed, even the form 

 of the wing (in a slight degree with Pieris napi, in a much 

 stronger degree, according to Edwards's sketches and figures, 

 with the American Grapta interrogation'} s \8i,Y. fahricii and var. 

 umhrosa). All the processes of the growth of the wing must, 

 therefore, be altered by it, and it is evident that this can no 

 longer happen, if the form of the wing already exists in a com- 

 plete state. 



However, before I pass on to the closer discussion of adaptive 

 seasonal dimorphism, I might cast a glance at the results on 

 Vanessa urticce. This species, indeed, is nowhere seasonally 

 dimorphic, but is certainly climatically polymorphic, i. e. it has 

 a dark polar form, var. polaris ; a bright red southern form, var. 

 ichnusa, with very small black spots, sometimes entirely absent ; 

 and an intermediate form which belongs to Central Europe. 

 These differences also seem to depend on the direct action of the 

 different temperature which affects the pupae. The existing 

 experiments, indeed, are still very incomplete ; above all, experi- 



■'= M. Standfuss, ' Ueber die Griinde der Variation und Aberration des 

 Falterstadiums bei den Schmetterlingen,' Leipzig, 1894. Sonderabzug aus 

 Insectenborse. E. Fischer, cand. med., ' Transmutation der Schmetter- 

 linge in Folge Temperaturveriinderungen,' Berlin, 1895. 



