1. Darwin: _Expression of Emotions in Men and Animals_; New York, 1899. 2. Starr: _Human Progress_; Pennsylvania, 1895. 3. Hartmann: _Anthropoid Apes_; New York, 1901. 4. Brehm: _From North Pole to Equator_; London, 1896. 5. Stanley: _In Darkest Africa_, vol i.; New York, 1890. 6. Romanes: _Animal Intelligence_; New York, 1899. 7. Evans: _Evolutional Ethics and Animal Psychology_; New York, 1898. 8. Jesse: _Gleanings in Natural History_, vol. i.; London, 1832. 9. Kropotkin: _Mutual Aid a Factor of Evolution_; New York, 1902. 10. Peckham and Peckham: _Instincts and Habits of the Solitary Wasps_; Madison, Wisconsin, 1898. IV. The Elements of Human and Non-human Mind Compared. The analysis of human mind and the comparison of its elements or powers with the powers of non-human mind corroborate the conclusions already arrived at through observation and deductive inference. The chief powers of the mind of man are _sensation_, _memory_, _emotion_, _imagination_, _volition_, _instinct_, and _reason_. All of these faculties are found in non-human beings, some of them developed to a much higher degree than they are in man, and some of them to a much lower. _Sensation_ is the effect produced on the mind when a sense organ is affected in some way by external stimuli. Sensation is the lumber of the mind, the raw material out of which are elaborated all other forms of consciousness. The chief species of sensation are those of sight, sound, smell, taste, and feeling. The original sense was feeling, and out of this sense were evolved the other four. The organs of seeing, hearing, smelling, and tasting are therefore modifications of the skin, which is the organ of original sense. The fact that in all animals, down almost to the very beginnings of life, sense organs exist, suggests that sensation may be almost, if not quite, coextensive with animal life. All mammals, birds, reptiles, amphibians, and fishes have the same special sense organs as man, and the organs of sight, sound, taste, and smell occupy in all vertebrates the same relative positions in the head. Birds see better than any other animals, and carnivora smell better. Ruminants see, hear, and smell with great acuteness. Fishes also see and hear well; and the wings of the bat are so exceedingly sensitive that it will move about blindfolded and with ears stopped with cotton almost as unerringly as when aided by sight and sound. Insects have smell, sight, and taste well developed, as is shown by their keen appreciation of the colours, perfumes, and flavours of flowers. They also hear. Stridulation proves this. Worms have eyes and ears, and land-leeches scent the approach of their prey at a long distance. The starfish and the medusa respond to all the five classes of stimuli which affect the five senses of man, and nervous substance is found in all animals above the sponge.