A study of his work leaves one with the conviction that, while these birds exhibit what we may call a nascent intelligence, their actions, on the whole, may be described as instinctive, or congenitally definite. That is to say, they follow one another in definite sequence. Hence we must regard each new phase in the chain of events appertaining to the reproductive cycle, as following one another in a definite sequence, so that any break therein throws the orderly performance of the necessary acts out of gear. There is no realization of what reproduction means, no deliberate striving to achieve that end. Each new phase brings its own set of associations and sets a new train of actions in motion, which are performed mechanically. For instance, these Warblers, like hosts of other species under similar circumstances, are scrupulously careful to remove the fæces of their young from the nest; thereby preserving it in a sanitary condition. It is certain that any neglect to do this would speedily end in the death of the young. This act is “instinctive”; it is not performed because the parents have evolved any views on sanitation, and any strain in whom this instinct was defective would speedily become eliminated. Mr. Howard has demonstrated the mechanical character of this sanitary measure by placing leaves in nests of young. The parents, having fed their offspring, at once seized upon the leaf and commenced to dispose of it after their usual fashion, first by trying to swallow it and then by carrying it away. They did not, evidently, realize the difference between the texture of the leaf and the milk-white, jelly-like envelope which always encloses the fæcal matter of the nestling. We shall probably never know how this most vitally important instinct came into being; nor can we hope to discover what chain of happenings begot the instinct, which each parent displays, to gently stimulate the cloacal lips of their offspring in order to induce the discharge of the fæces when this does not immediately follow the stimulus of swallowing food. We cannot credit these birds with notions on the importance of the regular discharge of the evacuations. Equally mysterious is the development of the envelope enclosing the fæcal matter. This is jelly-like in substance, and of considerable thickness, and is enclosed within a very delicate skin or pellicle, enabling one to lift the whole in the fingers without soiling them. How and where it is formed should not long evade discovery. But how it has come to be is another matter. We can, at any rate, vaguely account for responses of the organism to internal stimuli reacting directly on the individual, but here is an elaborate mechanism evolved in response to extra-personal needs: and which cannot be regarded as of exactly the same configuration as the instinct to feed the young.