4 o THE POPULAR SCIENCE MONTHLY. 



former enjoy. This similarity of individuals in relatively low 

 stages of development is accompanied by a lack of mental plia- 

 bility, a rigidity of custom, thought, and habit, that in turn leads 

 to the perpetuation of meaningless customs, to an unyielding con- 

 servatism, 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 re- 

 flex 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 unf oldment, 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 re- 

 peats inparvo 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 charac- 

 teristic of children is no less so of kittens, nor is their imitative- 

 ness 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 jeal- 

 ousy 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 emo- 

 tional 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 



