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    ON THE VARIATION OF SPECIES

    WITH ESPECIAL REFERENCE TO THE INSECTA;

    FOLLOWED BY AN INQUIRY INTO THE NATURE OF GENERA.

    BY

    T. VERNON WOLLASTON, M.A., F.L.S.


    "No compound of this earthly ball
    Is like another, all in all."

    TENNYSON.

    LONDON:

    JOHN VAN VOORST, PATERNOSTER ROW.

    1856.

"I do not enter so far into the province of the logicians as to take
notice of the difference there is between the _analytic_ and
_synthetic_ methods of coming at truth, or proving it;--whether it is
better to begin the disquisition from the subject, or from the
attribute. If by the use of _proper media_ anything can be showed to
be, or not to be, I care not from what term the demonstration or
argument takes its rise. Either way propositions may beget their like,
and more truth be brought into the world."--_Religion of Nature
Delineated_, p. 45 (A.D. 1722).


PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.


TO CHARLES DARWIN, ESQ., M.A., V.P.R.S.,

Whose researches, in various parts of the world, have added so much to
our knowledge of Zoological geography, this short Treatise is
dedicated.




PREFACE.


To make a dry subject entertaining, is impossible; but to render it,
at any rate, readable, has been my endeavour in the following pages.
How far I have succeeded in the experiment, it is not for me to
decide.

It having been suggested, by several of my friends, that it might be
desirable to bring together into a small compass some of the evidence
on Insect variation (with reference to external disturbing causes)
which my researches in the Madeira Islands have supplied me with, I
have been encouraged to do so: and I have added numerous conclusions
from other data also, which have from time to time fallen in my
way,--so as to confer on the volume a more practical interest, for
the general naturalist.

One of my main objects, however, has been to call attention to the
fact, that the Annulosa have not been hitherto sufficiently
considered, in the great questions arising out of the distribution of
animals and plants; hoping that, by so doing, some few of our British
entomologists, who have not looked into this branch of their science,
may be induced to enlist themselves in the cause of Insect geography.

If such a result be brought about; or if I be fortunate enough to open
for discussion any of the topics which have been touched upon, and so
lead to a more perfect solution of the problems which I have attempted
to explain, I shall consider myself more than repaid.

    10 Hereford Street, Park Lane, London.
                  May 10th, 1856.




                CONTENTS.


                CHAPTER I.
    Introductory Remarks

                CHAPTER II.
    Fact of Variation
          As a matter of experience
          As probable from analogy

                CHAPTER III.
    Causes of Variation
          Sec. 1. Climatal causes generally (whether dependent
               upon latitude or upon altitude)
          Sec. 2. Temporary heat or cold, of an unusual degree
          Sec. 3. Nature of the country, and of the soil
          Sec. 4. Isolation; and exposure to a stormy atmosphere

                CHAPTER IV.
    Organs and Characters of Variation

                CHAPTER V.
    Geological Reflections

                CHAPTER VI.
    The Generic Theory

                CHAPTER VII.
    Conclusion




CORRIGENDUM.


Page 90, for _Pecteropus Maderensis_ read _Pecteropus rostratus_.




SPECIFIC VARIATION IN THE INSECTA.




CHAPTER I.

INTRODUCTORY REMARKS.


A very small amount of information gained by the student in the field
of Nature is sufficient to kindle the desire to increase it. The more
we know, the more we are anxious to know; though the less we seem to
know. It is one of the distinctive privileges of the naturalist that
he has to labour in a mine which is inexhaustible: the deeper he digs
beneath the surface, the richer is the vein for excavation, and the
more interesting are the facts which he brings success