consider that poisonous snakes have been developed from harmless forms, and that many kinds of reptiles have lost limbs, teeth, and eyesight in the process of evolution. The present work is intended to appeal to two kinds of readers–to the field-naturalist, who, while interested in life-histories, habits, and geographical distribution, beauty or strangeness of forms, is indifferent to the homologies of the metasternum or similar questions;–and to the morphologist, who in his turn is liable to forget that his specimens were once alive. A great portion of the book is anatomical and systematic. It was necessary to treat anatomy, especially that of the skeleton, somewhat fully, since it has long been recognised that it is impossible to base a scientific classification upon external characters. The reader familiar with Vertebrate anatomy has a right to expect that questions of special morphological interest will be dwelt upon at length. Those who have no anatomical foundation must be referred to one of the now numerous introductory manuals on the subject. The account of the Amphibia is more complete than that of the Reptilia. It was possible to diagnose practically all the recent genera; and this has been especially done in the Anura, in order to show how in an otherwise very homogeneous group almost any part of the body, internal or external, can be modified in kaleidoscopic variety. The same could not be done with the Reptilia. Their principal groups,–called sub-classes in the present work, in order to emphasise their taxonomic importance in comparison with the main groups of Birds and Mammals,–differ so much from each other that it was decided to refrain {vii}from attempting a general account of them. Moreover, the number of species of recent lizards and snakes is so bewildering, the genera of many families being but tedious variations of the same theme, that only those forms have been described which are the most important, the most striking, or which the traveller is most likely to come across. The student who wishes to go farther into systematic details must consult the seven volumes of the _Catalogue of Reptiles in the British Museum_ (London, 1889-1896). Mr. G. A. Boulenger, the author of this magnificent series, has rendered the systematic treatment of recent Amphibia and Reptiles an easy task. During many years of the most friendly intercourse I have profited on countless occasions by his ever-ready advice. Although he has kindly read the proofs of the part dealing with the Amphibia it would be unfair to associate him with any of its shortcomings or with contestable opinions, for which I alone am responsible. Cope's large work on the Crocodilians, Lizards, and Snakes of North America (_Rep. U.S. Nat. Mus. for 1898_ (1900)) has unfortunately appeared too late to be used in the present work.