Transcriber’s notes: The text of this e-book has mostly been preserved in its original form, but a number of typographic errors have been corrected silently – they are listed at the end of the book. Missing or inconsistent punctuation has been corrected silently in a few places, but inconsistent hyphenation has not been altered. An index item that lacked a page reference has been remedied, and an archaic symbol representing the mathematical ‘factorial’ function has been replaced by the standard exclamation mark (!). Footnotes have been numbered and positioned below the relevant paragraphs. The marker for footnote 31 was missing from the original text and has been arbitrarily placed at the end of the relevant paragraph. In this plain text version, italic text is denoted by _underscores_. Superscripted characters are surrounded by curly brackets preceded by a caret symbol, e.g. 2^{10}, and subscripted characters are surrounded by curly brackets preceded by a downward arrow, e.g. ↓{H}. THE PHILOSOPHY OF BIOLOGY CAMBRIDGE UNIVERSITY PRESS London: FETTER LANE, E.C. C. F. CLAY, Manager [Illustration] Edinburgh: 100 PRINCES STREET Berlin: A. ASHER AND CO. Leipzig: F. A. BROCKHAUS New York: G. P. PUTNAM’S SONS Bombay and Calcutta: MACMILLAN AND CO., LTD. Toronto: J. M. DENT & SONS, LTD. Tokyo: THE MARUZEN-KABUSHIKI-KAISHA _All rights reserved_ THE PHILOSOPHY OF BIOLOGY BY JAMES JOHNSTONE, D.Sc. Cambridge: at the University Press 1914 INTRODUCTION