THE PRINCIPLES OF
BIOLOGY

BY

HERBERT SPENCER

IN TWO VOLUMES
VOL. II

REVISED AND ENLARGED EDITION
1899

NEW YORK
D. APPLETON AND COMPANY
1900

Copyright, 1867, 1899,
By D. APPLETON AND COMPANY.

[v]

PREFACE
TO THE REVISED AND ENLARGED EDITION OF VOL. II.

To the statements made in the preface to the first volume of thisrevised edition, there must here be added a few having specialreference to this second volume.

One of them is that the revision has not been carried out in quite thesame way, but in a way somewhat less complete. When reviewing the firstvolume a friendly critic, Prof. Lloyd Morgan, said:—

“But though the intellectual weight has also been augmented,it is an open question whether it would not have been wiserto leave intact a treatise, &c... relegating corrections andadditions to notes and appendices.”

I think that Prof. Morgan is right. Though at the close of the prefaceto volume I, I wrote:—“in all sections not marked as new, theessential ideas set forth are the same as they were in the originaledition of 1864,” yet the reader who has not read this statement,or does not bear it in mind, will suppose that all or most of theenunciated conceptions are of recent date, whereas only a small part ofthem are. I have therefore decided to follow, in this second volume, acourse somewhat like that suggested by Prof. Morgan—somewhat like, Isay, because in sundry cases the amendments could not be satisfactorilymade by appended notes.

[vi]

But there has been a further reason for this change of method. Aninvalid who is nearly eighty cannot with prudence enter upon work whichwill take long to complete. Hence I have thought it better to make theneedful alterations and additions in ways requiring relatively moderatetime and labour.

The additions made to this volume are less numerous and less importantthan those made to the first volume. A new chapter ending Part V, on“The Integration of the Organic World,” serves to round off the generaltheory of Evolution in its application to living things. Beyond a newsection (§ 289a) and the various foot-notes, serving chiefly thepurpose of elucidation, there are notes of some significance appendedto Chapters I, III, IV, and V, in Part IV, Chapters V and VIII, in PartV, and Chapters IX, X, and XII in Part VI. Moreover there are threefurther appendices, D2, F, and G, which have, I think, considerablesignificance as serving to make clearer some of the views expressed inthe body of the work.

Turning from the additions to the revisions, I have to say that theaid needed for bringing up to date the contents of this volume, hasbeen given me by the gentlemen who gave me like aid in revising thefirst volume: omitting Prof. Perkin, within whose province none of thecontents of this volume fall. Plant-Morphology and Plant-Physiologyhave been overseen by Mr. A. G. Tansley. Criticisms upon parts dealingwith Animal Morphology I owe to Mr. J. T. Cunningham and Prof. E. W.MacBride. And the statements included under Animal Physiology have beenchecked by Mr. W. B. Hardy.

[vii]

For reasons like those named in the preface to the first volume, Ihave not submitted the proofs of

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