Studies in the Theory of Descent, Volume II

Transcriber’s notes
Cover created by Transcriber and placed into the Public Domain.
Pages 1–400, Plates I–II, and some referenced footnotes are in Volume I. Links to them may not work with some reading devices.
BY DR. AUGUST WEISMANN PROFESSOR IN THE UNIVERSITY OF FREIBURG
WITH NOTES AND ADDITIONS BY THE AUTHOR
TRANSLATED AND EDITED, WITH NOTES, BY RAPHAEL MELDOLA, F.C.S. LATE VICE-PRESIDENT OF THE ENTOMOLOGICAL SOCIETY OF LONDON
WITH A PREFATORY NOTICE BY CHARLES DARWIN, LL.D., F.R.S. Author of “The Origin of Species,” &c.
IN TWO VOLUMES VOL. II.
WITH EIGHT COLOURED PLATES

It would be meaningless to assert that the two stages above mentioned were completely independent of one another. It is obvious that the amount of organic and living matter contained in the caterpillar determines the size of the butterfly, and that the quantity of organic matter in the egg must determine the size of the emergent larva. The assertion in the above heading refers only to the structure; but even for this it cannot be taken as signifying an absolute, but only a relative independence, which, however, certainly obtains in a very high degree. Although it is conceivable that every change of structure in the imago may entail a correlative change of structure in the larva, no such cases have as yet been proved; on the contrary, all facts indicate an almost complete independence of the two stages. It is quite different with cases of indirect dependence, such, for example, as are brought about by ‘nurse-breeding.’ This phenomenon is almost completely absent in Lepidoptera, but is found in Diptera, and especially in Hymenoptera in every degree. The larvæ of ichneumons which live in other insects, require (not always, but in most instances) that the female imago should possess a sharp ovipositor, so that in this case also the structure and mode of life of the larva influences the perfect insect. This does not depend, however, on inherent laws of growth (correlation), but on the action of external influences, to which the organism endeavours to adapt itself by natural selection.