given to the world is probably the most trustworthy and instructive that has yet been contributed to that science. There has been a copious literature of anecdote designed to illustrate the mental capacities of the most intelligent members of the animal series—as the dog, the elephant, the monkey, and the ant; but while, on the one hand, the statements have often been so extravagant as to awaken incredulity, on the other there has been but little exposition of principles which would enable the reader to judge of the truth or error of current representations. The interest in the subject has always been great, and, with the prevailing lax habits of criticising evidence, many stories have passed into circulation, and been accepted, which would hardly bear examination. It was eminently desirable, therefore, and for scientific purposes imperative, that the popular statements should be rigorously sifted, in order that we may find out what may be relied upon as true. It is obvious that only the thoroughly prepared psychologist is competent for such work, and many years of study in this field have well qualified Mr. Romanes to undertake it.
The present volume is in a certain sense complete in itself; and from another point of view it is but a foundation, which is yet to have its superstructure. It has long been the author's intention to write a treatise upon comparative psychology, in the light of the doctrine of evolution, and his intention was to treat the whole subject in a single work. His preliminary inquiry was, of course, into the facts upon which such a view must rest, but he found his materials so extensive, and in themselves so important, that he was compelled to arrange for two separate books; the first to be made up of the observed facts, carefully collated and classified, so as to give the grades of intelligence actually reached in the various groups of the animal kingdom, and to leave for a second volume the problem of psychical development to be derived from these data. The present book on "Animal Intelligence" is the first, and is mainly descriptive, while the second, to be built upon it, will be more analytic and philosophic.
Undoubtedly the present volume will have the highest interest for general readers, as it involves no speculation or abstruse reasoning, and aims only at descriptions and discriminating estimates of the degree of intelligence manifested in the different groups of animate creatures.
But while Mr. Romanes has closely sifted his materials, so as to furnish only authenticated facts, it would be a great mistake to suppose that his pages are less entertaining than the loose compilations with which we have been familiar upon this subject. The phenomena are equally surprising and wonderful, but with the further advantage that we have a fair confidence in their reality. The intelligence displayed by the inferior animals is often well calculated to awaken astonishment, and we are free to confess that some of Mr. Romanes's stories would excite incredulity if we had not a pretty strong confidence in his caution, and if the special manifestations alleged were not confirmed by other and similar observations. To the general reader, the book will prove a fund of interest on one of the most fascinating of subjects, and to the student of natural history it will have a scientific value as affording a sound basis for the formation of conclusions respecting the psychical capacities of animals.
In regard to the vexed question of mind and instinct in the lower animals, of which so much has been written, the author lays down at the outset the principle that he will follow in determining mental gradation, and this may be gathered from the following remarks in his introduction:
"The criterion of mind, therefore, which I propose, and to which I shall adhere throughout the present volume, is as follows: Does the organism learn to make new adjustments, or to modify old ones, in accordance with the results of its own individual experience?. . . I may, however, here explain that in my use of this criterion I shall always regard it as fixing only the upper limit of non-mental action; I shall never regard it as fixing the lower limit of mental action. . . . In other words, because a lowly-organized animal does not learn by its own individual experience, we may not therefore conclude that, in performing its natural or ancestral adaptations to appropriate stimuli, consciousness, or the mind-element, is wholly absent; we can only say that this element, if present, reveals no