end we shall regard behaviour which has “become mechanized in the course of individual life” as due to acquired habit, reserving the term _instinctive_ for such behaviour as is independent of individual experience. We shall, in short, so far accept Spence’s definition. In this definition, as in those of the majority of naturalists, it seems to be further implied that instinctive behaviour is of a relatively definite kind, though it is no doubt subject to such variation as is found in animal structure and organization. Mr. Rutgers Marshall, however, in a recent work,[27] protests against any such implication, and urges that “this variableness is so wide that definiteness of reaction cannot for a moment be used as a differentia in relation to instinct without narrowing our conception of the bounds of instinct in a manner to be deplored.” “The actions,” he says, “connected with the preparation for self-defence, those connected with protection of the young, with nest-building, with migration, etc., these actions are surely to be classed as instinctive; and yet they are exceedingly variable and unpredictable in detail; all that we can predict is the general trend of the varying actions which result from varying stimuli under varying conditions, and which function to some determinate biological end.” Mr. Marshall then proceeds to argue that we are “warranted in speaking of the ethical instincts, of the patriotic instincts, of the benevolent instincts, and of the artistic instincts;” and thus leads up to the position, to be further elaborated in his work, that there exists in man a religious instinct which has fulfilled a function of biological value in the development of our race. Now, here again there is much in popular usage of the words _instinct_ and _instinctive_ which lends support, for what it is worth, to Mr. Marshall’s very broad conception of the range of instinct. Again and again we hear, in the pulpit and elsewhere, of the religious instinct; we hear, too, of the benevolent, patriotic, and artistic instincts, and more besides. But what we are endeavouring to define is a type of behaviour which, as such, is prior to instruction and experience. Can we affirm that patriotic and religious behaviour conforms to such a type? Is it unquestionably congenital and not acquired? If we are forced to give negative answers to these questions we must regard Mr. Marshall’s conception of instinct (one inclusive of multifarious tendencies which have a biological value) as too broad and too vague to be of any service to us at this stage of our study of animal behaviour.