former enjoy. This similarity of individuals in relatively low stages of development is accompanied by a lack of mental pliability, a rigidity of custom, thought, and habit, that in turn leads to the perpetuation of meaningless customs, to an unyielding conservatism, an uncertain and fitful advance. And we may add that the development of the parental feelings and virtues seems clearly richer in highly developed races than in undeveloped ones. We may epitomize our thought in Mr. Spencer's words: "The animal kingdom at large yields us reasons for associating an inferior and more rapidly completed mental type with a relatively automatic nature. Lowly organized creatures guided almost entirely by reflex actions, are in but small degrees changeable by individual experiences. . . . Inferior and superior races are contrasted in this respect. Many travelers comment on the unchangeable habits of savages. The semi-civilized nations of the East, past and present, were or are characterized by a greater rigidity of custom than characterizes the more civilized nations of the West. . . . And if we contrast classes or individuals around us, we see that the most developed in mind are the most plastic."
I have dwelt long upon this argument because it illustrates so well the closely analogous developments of these three paths of mental unfoldment, inferences traceable from facts gathered along one of the lines finding corroboration along the others, and all contributing to the significance of the dictum that the child repeats in parvo the history of the descent of man, and of the growth of the human race.
Resuming at this point our comparison of animal with infant traits, we have learned to expect mental similarity only in such animals as in their adult condition surpass at least in certain respects the capabilities of the human infant at birth. Within this range we find abundant points of community of various degrees of value and familiarity. The playfulness that is characteristic of children is no less so of kittens, nor is their imitativeness more typical than that from which the word "to ape" has been derived. Curiosity, inventiveness, dislike of ridicule, love of being fondled, craving for attention, with the resulting jealousy and anger when such attention is refused, are types of more complex emotions common to intelligent animals and children. Indeed, the terms of familiarity so often found and so easily established between children and their pets can not but be based, in part at least, upon a deep sympathy and community of emotional life. On the intellectual side correspondences are no less frequent and significant, but are difficult to describe and analyze. M. Perez, a discerning student of children, has carefully recorded the life histories and early trials of two pet kittens, and found constant occasion to draw analogies between the kittens and the