But in his structure and functions man bears, as is now well known, a marked resemblance to the lower animals. His respiratory and digestive organs, for example, may be duplicated as far down in the animal scale as birds and chickens.[2] Man's whole physical apparatus and mode of life, save in complexity and refinement of operations, are the same as those of any of the higher mammals. But more important for the student of human behavior, man's mental life--that is, his way of responding to and dealing with his environment--is in large part identical with that of the lower animals, especially of the most highly developed vertebrates, such as the monkey. They have, up to a certain point, precisely the same equipment for adjusting themselves to the conditions of life. Apart from education, both man and animal are endowed with a set of more or less fixed tendencies to respond in specific ways to specific stimuli. These inborn or congenital tendencies are generally known as reflexes or instincts.[1] These are unlearned ways, exhibited by both human and animal organisms, of responding promptly and precisely, and in a comparatively changeless manner to a given stimulus from the environment. These tendencies to act, while they may be, and most frequently are of advantage to the organism, are not conscious or acquired. They are irresistible impulses to do just such-and-such particular things in such-and-such particular ways when confronted with just such-and-such particular situations. In the well-known words of James: [Footnote 2: With certain modifications accounted for in their historical "descent" with modification from a common ancestor. See Scott: _Theory of Evolution_.] [Footnote 1: The difference between the two is largely one of complexity. By a reflex is meant a very simple and comparatively rigid response; by an instinct a series of reflexes such that when the first is set off, the remainder are set off in a regularly determinate succession.] The cat runs after the mouse, runs or shows fight before the dog, avoids falling from walls and trees, shuns fire and water, etc., not because he has any notion either of life or death, or of self-preservation. He has probably attained to no one of these conceptions in such a way as to react definitely upon it. He acts in each case separately, and simply because he cannot help it; being so framed that when that particular running thing called a mouse appears in his field of vision he _must_ pursue; that when that particular barking and obstreperous thing called a dog appears there he _must_ retire, if at a distance, and scratch if close by; that he _must_ withdraw his feet from water, and his face from flame.[2] [Footnote 2: James: _Psychology_, vol. II, p. 384.]