Chapter I: 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.