Studies in the Theory of Descent. Degeneration. A Chapter in Darwinism

Abstract

THE first of Dr. Weismann's “Studies,” of which Mr. Meldola has given us an excellent translation, with the author's latest notes and additions, is devoted to a thorough examination of the well-known but hitherto little understood phenomenon of the seasonal forms of butterflies. For the benefit of those unacquainted with entomology we may state, that many butterflies have two, or even three broods in a year. One brood appears in spring, their larvæ having fed during the preceding autumn and passed the winter in the pupa state, while the others appear later in the year, having passed rapidly through all their transformations and thus never having been exposed to the cold of winter. In most cases the insects produced under these opposite conditions present little or no perceptible difference; but in others there is a constant variation, and sometimes this is so great that the two forms have been described as distinct species. The most remarkable case among European butterflies is that of Araschnia prorsa, the winter or spring form of which was formerly considered to be a distinct species and named Araschnia levana. The two insects differ considerably in both sexes, in markings, in colour, and even in the form of the wings, so that till they were bred and found to be alternate broods of the same species (about the year 1830) no one doubted their being altogether distinct.

Studies in the Theory of Descent.

By Dr. Aug. Weismann, Professor in the University of Freiburg. Translated and Edited by Raphael Meldola, F.C.S., Secretary of the Entomological Society of London. Part 1. On the Seasonal Dimorphism of Butterflies, with Two Coloured Plates. (London: Sampson Low, Marston, and Co., 1880.)

Degeneration. A Chapter in Darwinism.

By Prof. E. Ray Lankester NATURE Series. (Macmillan and Co., 1880.)