the case. The districts in which Levana occurs on the Yenisei have about the same isotherm as Archangel or Haparanda, and therefore the same summer temperature. Dr. Staudinger, whose views I solicited, writes to me: – “In Finnmark (about 67° N.) I observed no species with two generations; even Polyommatus Phlæas, which occurs there, and which in Germany has always two, and in the south, perhaps, three generations, in Finnmark has only one generation. A second generation would be impossible, and this would also be the case with Levana in the middle of Yenisei. I certainly have Levana and Prorsa from the middle of Amur, but Levana flies there at the end of May, and the summers are very warm.” The middle of Amur lies, moreover, in 50° N. lat., and therefore 10°-13° south of the districts of the Yenisei mentioned.
It must thus be certainly admitted that on the Yenisei A. Levana occurs only in the Levana form, and that consequently this species is at the present time, in the northernmost portion of its area of distribution, in the same condition as that in which I conceive it to have been in mid Europe during the glacial period. It would be of the greatest interest to make experiments in breeding with this single-brooded Levana from the Yenisei, i.e., to attempt to change its offspring into the Prorsa form by the action of a high temperature. If this could not be accomplished it would furnish a confirmation of my hypothesis than which nothing more rigorous could be desired.]
When Dorfmeister remarks that hibernating pupæ which, at an early stage “were taken for development into a room, or not exposed to any cold, gave dwarfed, weakly and crippled,” or otherwise damaged butterflies, this is entirely attributable to the fact that this able entomologist had neglected to supply the necessary moisture to the warm air. By keeping pupæ over water I have always obtained very fine butterflies.
20
[For other remarkable cases of sexual dimorphism (not antigeny in the sense used by Mr. S. H. Scudder, Proc. Amer. Acad., vol. xii. 1877, pp. 150–158) see Wallace “On the Phenomena of Variation and Geographical Distribution, as illustrated by the Papilionidæ of the Malayan Region,” Trans. Linn. Soc., vol. xxv. 1865, pp. 5–10. R.M.]
21
[Eng. ed. Dimorphism of this kind has since been made known: the North American Limenitis Artemis and L. Proserpina are not two species, as was formerly believed, but only one. Edwards bred both forms from eggs of Proserpina. Both are single-brooded, and both have males and females. The two forms fly together, but L. Artemis is much more widely distributed, and more abundant than L. Proserpina. See “Butterflies of North America,” vol. ii.]
22
[Eng. ed. Edwards has since proved experimentally that by the application of ice a large proportion of the pupæ do indeed give rise to the var. Telamonides. He bred from eggs of Telamonides 122 pupæ, which, under natural conditions, would nearly all have given the var. Marcellus. After two months’ exposure to the low temperature there emerged from August 24th to October 16th, fifty butterflies, viz. twenty-two Telamonides, one intermediate form between Telamonides and Walshii, eight intermediate forms between Telamonides and Marcellus more nearly related to the former, six intermediate forms between Telamonides and Marcellus, but more closely resembling the latter, and thirteen Marcellus. Through various mishaps the action of the ice was not complete and equal. See the “Canadian Entomologist,” 1875, p. 228. In the newly discovered case of Phyciodes Tharos also, Edwards has succeeded in causing the brood from the winter form to revert, by the application of ice to this same form. See Appendix II. for a résumé of Edwards’ experiments upon both Papilio Ajax and Phyciodes Tharos. R.M.]
23
Thus from eggs of Walshii, laid on April 10th, Edwards obtained, after a pupal period of fourteen days, from the 1st to the 6th of June, fifty-eight butterflies of the form Marcellus, one of Walshii, and one of Telamonides.
24
[The word ‘Amixie,’ from the Greek ἀμιξία, was first adopted by the author to express the idea of the prevention of crossing by isolation in his essay “Über den Einfluss der Isolirung auf die Artbildung,” Leipzig, 1872, p. 49. R.M.]
25
[Eng. ed. In 1844, Boisduval maintained this relationship of the two forms. See Speyer’s “Geographische Verbreit. d. Schmetterl.,” i. p. 455.]
26
According to a written communication from Dr. Staudinger, the female Bryoniæ from Lapland are never so dusky as is commonly the case in the Alps, but they often have, on the other hand, a yellow instead of a white ground-colour. In the Alps, yellow specimens are not uncommon, and in the Jura are even the rule.
27
[According to W. F. Kirby (Syn. Cat. Diurn. Lepidop.), the species is almost cosmopolitan, occurring, as well as throughout Europe, in Northern India (var. Timeus), Shanghai (var. Chinensis), Abyssinia (var. Pseudophlæas), Massachusetts (var. Americana), and California (var. Hypophlæas). In a long series from Northern India, in my own collection, all the specimens are extremely dark, the males being almost black. R.M.]
28
[Eng. ed. From a written communication from Dr. Speyer, it appears that also in Germany there is a small difference between the two generations. The German summer brood has likewise more black on the upper side, although seldom so much as the South European summer brood.]
29
[Assuming that in all butterflies similar colours are produced by the same chemical compounds. R.M.]
30
[Mr. H. W. Bates mentions instances of local variation in colour affecting many distinct species in the same district in his memoir “On the Lepidoptera of the Amazon Valley;” Trans. Linn. Soc., vol. xxiii. Mr. A. R. Wallace also has brought together a large number of cases of variation in colour according to distribution, in his address to the biological section of the British Association at Glasgow in 1876. See “Brit. Assoc. Report,” 1876, pp. 100–110. For observations on the change of colour in British Lepidoptera according to distribution see papers by Mr. E. Birchall in “Ent. Mo. Mag.,” Nov., 1876, and by Dr. F. Buchanan White, “Ent. Mo. Mag.,” Dec., 1876. The colour variations in all these cases are of course not protective as in the well-known case of Gnophos obscurata, &c. R.M.]
“On the Origin and Metamorphoses of Insects,” London, 1874.
33
I at first thought of designating the two forms of cyclical or homochronic heredity as ontogenetic- and phyletic-cyclical heredity. The former would certainly be correct; the latter would be also applicable to alternation of generation (in which actually two or more phyletic stages alternate with each other) but not to all those cases which I attribute to heterogenesis, in which, as with seasonal dimorphism, a series of generations of the same phyletic stage constitute the point of departure.
34
When Meyer-Dürr, who is otherwise very accurate, states in his “Verzeichniss der Schmetterlinge der Schweiz,” (1852, p. 207), that the winter and summer generations of P. Ægeria differ to a small extent in the contour of the wings and in marking, he has committed an error. The characters which this author attributes to the summer form are much more applicable to the female sex. There exists in this species a trifling sexual dimorphism, but no seasonal dimorphism.
35
P. C. Zeller, “Bemerkungen über die auf einer Reise nach Italien und Sicilien gesammelten Schmetterlingsarten.” Isis, 1847, ii. –
