Studies in the Theory of Descent

Abstract

THE first part of this work, devoted to an examination of the phenomena of seasonal dimorphism in butterflies, was noticed a little more than a year ago (NATURE, vol. xxii. p. 141). We now have a second instalment of much greater bulk, comprising two separate essays. In the first and most important of these Dr. Weismann gives us the results of a detailed study of the changes in the markings of the caterpillars of the Sphingidæ during the course of their growth and development, and enters at great length into the various questions to which the phenomena observed give rise. Accepting the doctrine that the ontogeny or development of the individual gives us a more or less accurate notion of the phylogeny or course of development of the race, he endeavours with some success to determine the ancestral forms of the various genera of the Sphingidæ by means of the successive changes of form and coloration of the larvæ. The main facts which he has here established are, that all the larvæ are born of a uniform tint—that the first markings are longitudinal lines—that the oblique lines when they exist always appear later, and the ringed or ocellated spots last of all. Great changes of colour also occur in some species, but all the more important changes, whether of colour or marking, only take place after the larvæ have acquired a considerable size. From the whole assemblage of facts in this branch of the inquiry he deduces the following three laws of development:—

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. Part II. On the Origin of the Markings of Caterpillars. On Phyletic Parallelism in Metamorphic Species. With Six Coloured Plates. (London: Sampson Low, Marston, Searle, and Rivington, 1881.)