CHAP. I- SERVICEABLE ASSOCIATED HABITS. 47 lieved by some naturalists to be specifically extinct), when comfortably lying on a warm shawl or other soft substance, to pound it quietly and alternately with their fore-feet; their toes being spread out and claws slightly protruded, precisely as when sucking their mother. That it is the same movement is clearly shown by their often at the same time taking a bit of the shawl into their mouths and sucking it; generally closing their eyes and purring from delight. This curious move- ment is commonly excited only in association with the sensation of a warm soft surface; but I have seen an old cat, when pleased by having its back scratched, pounding the air with its feet in the same manner; so that this action has almost become the expression of a pleasurable sensation. Having referred to the act of sucking, I may add that this complex movement, as well as the alternate protrusion of the fore-feet, are reflex actions; for they are performed if a finger moistened with milk is placed in the mouth of a puppy, the front part of whose brain has been removed.17 It has recently been stated in France, that the action of sucking is excited solely through the sense of smell, so that if the olfactory nerves of a puppy are destroyed, it never sucks. In like man- ner the wonderful power which a chicken possesses only a few hours after being hatched, of picking up small particles of food, seems to be started into action through the sense of hearing; for with chickens hatched by arti- ficial heat, a good observer found that "making a noise •with the finger-nail against a board, in imitation of the hen-mother, first taught them to peck at their meat." 18 17 Carpenter, ' Principles of Comparative Physiology,' 1854, p. 690, and Miiller's * Elements of Physiology,' Bug. translat. vol. ii. p. 936. 18 Mowbray on ' Poultry/ 6th edit. 1830, p. 54.