Transcriber’s notes
Cover created by Transcriber and placed into the Public Domain.
Pages 1–400, Plates I–II, and some referenced footnotesare 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
London:
SAMPSON LOW, MARSTON, SEARLE, & RIVINGTON
CROWN BUILDINGS, 188, FLEET STREET
1882
[All rights reserved]
It would be meaningless to assert that the twostages above mentioned were completely independentof one another. It is obvious that the amountof organic and living matter contained in the caterpillardetermines the size of the butterfly, and thatthe quantity of organic matter in the egg must determinethe size of the emergent larva. The assertionin the above heading refers only to thestructure; but even for this it cannot be taken assignifying an absolute, but only a relative independence,which, however, certainly obtains in avery high degree. Although it is conceivablethat every change of structure in the imago mayentail a correlative change of structure in the larva,no such cases have as yet been proved; on thecontrary, all facts indicate an almost complete independenceof the two stages. It is quite differentwith cases of indirect dependence, such, for example,as are brought about by ‘nurse-breeding.’ Thisphenomenon is almost completely absent in Lepidoptera,402but is found in Diptera, and especially inHymenoptera in every degree. The larvæ ofichneumons which live in other insects, require(not always, but in most instances) that the femaleimago should possess a sharp ovipositor, so thatin this case also the structure and mode of life ofthe larva influences the perfect insect. This doesnot depend, however, on inherent laws of growth(correlation), but on the action of externalinfluences, to which the organism endeavours toadapt itself by natural selection.
I will now let the facts speak for themselves.
It is shown by those species in which only onestage is di- or polymorphic that not every changein the one stage entails a corresponding changein the other. Thus, in all seasonally dimorphicspecies we find that the caterpillars of butterflieswhich are often widely different in the colourand marking of their successive generations areabsolutely identical. On the other hand, manyspecies can be adduced of which the larvæ aredimorphic whilst the imagines occur only in oneform (compare the first and second essays in thisvolume).
There are however facts which directly provethat any one stage can change independently ofthe ot