Mr. Wells' little book is avowedly written for examination purposes, and in conformity with the requirements of the now familiar "type system" of teaching. Recent attempts have been made to depreciate this. While affording a discipline in detailed observation and manipulation second to that of no other branch of learning, it provides for that "deduction" and "verification" by which all science has been built up; and this appears to me ample justification for its retention, as the most rational system which can be to-day adopted. Evidence that its alleged shortcomings are due rather to defective handling than to any inherent weakness of its own, would not be difficult to produce. Although rigid in its discipline, it admits of commentatorial treatment which, while heightening the interest of the student, is calculated to stimulate alike his ambition and his imagination. That the sister sciences of Botany and Zoology fall under one discipline, is expressed in the English usage of the term "Biology." Experience has shown that the best work in either department has been produced by those who have acquired on all-round knowledge of at least the elementary stages of both; and, that the advanced morphologist and physiologist are alike the better for a familiarity with the principles-- not to say with the progressive advancement-- of each other's domain, is to-day undeniable. These and other allied considerations, render it advisable that the elementary facts of morphology and physiology should be presented to the beginner side by side-- a principle too frequently neglected in books which, like this one, are specially written for the biological neophyte. Although the student is the wiser for the actual observation of the fact of nature, he becomes the better only when able to apply them, as for example, by the judicious construction of elementary generalizations, such as are introduced into the pages of this work. So long as these generalizations, regarded as first attempts to deduce "laws" in the form of "generalized statement of facts based observation," are properly introduced into an elementary text-book, intended for the isolated worker cut off from the lecture room, their intercalation is both healthy and desirable. Mr. Wells has kept these precepts constantly in mind in the preparation of his work, and in the formulation of his plans for its future extension, thereby enhancing the value of the book itself, and at the same time, discouraging the system of pure cram, which is alien to the discipline of biological science. G. B. Howes Royal College of Science, South Kensington; November 30, 1892. -Preface_