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Pages 401-729 and Plates III-VIII are in Volume II.




STUDIES IN THE THEORY OF DESCENT.




  LONDON:
  PRINTED BY GILBERT AND RIVINGTON, LIMITED,
  ST. JOHN’S SQUARE,




  STUDIES IN THE THEORY
  OF DESCENT

  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. I.

  WITH EIGHT  PLATES

  London:

  SAMPSON LOW, MARSTON, SEARLE, & RIVINGTON
  CROWN BUILDINGS, 188, FLEET STREET

  1882

  [_All rights reserved._]




PREFATORY NOTICE.


The present work by Professor Weismann, well known for his profound
embryological investigations on the Diptera, will appear, I believe, to
every naturalist extremely interesting and well deserving of careful
study. Any one looking at the longitudinal and oblique stripes, often
of various and bright colours, on the caterpillars of Sphinx-moths,
would naturally be inclined to doubt whether these could be of the
least use to the insect; in the olden time they would have been called
freaks of Nature. But the present book shows that in most cases the
colouring can hardly fail to be of high importance as a protection.
This indeed was proved experimentally in one of the most curious
instances described, in which the thickened anterior end of the
caterpillar bears two large ocelli or eye-like spots, which give to
the creature so formidable an appearance that birds were frightened
away. But the mere explanation of the colouring of these caterpillars
is but a very small part of the merit of the work. This mainly consists
in the light thrown on the laws of variation and of inheritance by
the facts given and discussed. There is also a valuable discussion
on classification, as founded on characters displayed at different
ages by animals belonging to the same group. Several distinguished
naturalists maintain with much confidence that organic beings tend to
vary and to rise in the scale, independently of the conditions to which
they and their progenitors have been exposed; whilst others maintain
that all variation is due to such exposure, though the manner in which
the environment acts is as yet quite unknown. At the present time
there is hardly any question in biology of more importance than this
of the nature and causes of variability, and the reader will find in
the present work an able discussion on the whole subject, which will
probably lead him to pause before he admits the existence of an innate
tendency to perfectibility. Finally, whoever compares the discussions
in this volume with those published twenty years ago on any branch of
Natural History, will see how wide and rich a field for study has been
opened up through the principle of Evolution; and such fields, without
the light shed on them by this principle, would for long or for ever
have remained barren.

            CHARLES DARWIN.




TRANSLATOR’S PREFACE.


In offering to English readers this translation of Professor Weismann’s
well-known “Studies in the Theory of Descent,” the main part of which
is devoted to entomological subjects, I have been actuated by the
desire of placing in the hands of English naturalists one of the most
complete of recent contributions to the theory of Evolution as applied
to the elucidation of certain interesting groups of facts offered by
the insect world. Although many, if not most, working naturalists
are already familiar with the results of Dr. Weismann’s researches,
of which abstracts have from time to time appeared in English and
American scientific journals, I nevertheless believe that a study
of the complete work, by enabling the reader to follow closely the
detailed lines of reasoning and methods of experiment employed by the
author, will be found to be of considerable value to those biologists
who have not been able to follow the somewhat difficult phraseology of
the original. It is not my intention, nor would it be becoming in me to
discuss here the merits of the results arrived at by the minute and
laborious investigations with which Dr. Weismann has for many years
occupied himself. I may however point out that before the appearance of
the present work the author, in addition to his well-known papers on
the embryology and development of insects, had published two valuable
contributions to the theory of descent, viz. one entitled “Über die
Berechtigung der Darwin’schen Theorie” (1868), and another “Über den
Einfluss der Isolirung auf die Artbildung” (1872). These works, which
are perhaps not so well known in this country as could be desired,
might be advantageously studied in connection with the present volume
wherein they are frequently referred to.

Since every new contribution to science is a fresh starting-point for
future work, I may venture without any great breach of propriety to
dwell briefly upon one or two of the main points which appear to me to
be suggested by Prof. Weismann’s investigations.

Although the causes of Glacial Epochs is a subject which has much
occupied the attention of geologists and physiographers, the question
is one of such great complexity that it cannot yet be regarded as
finally settled. But apart