It is on this account that the term “generic image” would in my opinion be preferable for describing cases of this character. “I have frequently seen not only dogs, but horses, mules, cattle, and goats, go in search of water in places which they had never visited before. They are guided by general principles, because they go to these watering places at times when the latter are perfectly dry.”[13] Undoubtedly it may be objected that association of images here plays a preponderating part. The sight of the hollows recalls the water which, though absent, forms part of a group of sensations which has been perceived many times; but since the generic image is, as we shall see later, no more than an _almost passive_ condensation of resemblances, these facts clearly indicate its nature and its limits. I shall merely allude without detailed comment to the numerous observations on the aptitude of dogs and cats for finding means to accomplish their aims, the anecdotes of their mechanical skill, and the ruses (so well described by G. Leroy) which the fox and the hare employ to outwit the hunter, “when they are old and schooled by experience; since it is to their knowledge of facts that they owe their exact and prompt inductions.” The most intelligent of all animals, the higher orders of monkeys, have not been much studied in their wild state, but such observations as have been made, some of which have been contributed by celebrated naturalists, fix with sufficient distinctness the intellectual level of the better endowed. The history of Cuvier’s orang-outang has been quoted to satiety. The more recent books on comparative psychology contain ample testimony to their ability to profit by experience[14] and to construct instruments. A monkey, not having the strength to lift up the lid of a chest, employed a stick as a lever. “This use of a lever as a mechanical instrument is an action to which no animal other than a monkey has ever been known to attain.” Another monkey observed by Romanes, also “succeeded by methodical investigation, _without assistance_, in discovering for himself the mechanical principle of the screw; and the fact that monkeys well understand how to use stones as hammers, is a matter of common observation.” They are also skilful in combining their stratagems, as in the case of one who, being held captive by a chain, and thus unable to reach a brood of ducklings, held out a piece of bread in one hand, and on tempting a duckling within his reach, seized it by the other, and killed it with a bite in the breast.[15] One mental operation remains which must be examined separately, and in its study we shall pursue the same method, wherever it occurs, throughout this work. The process in question has the advantage of being perfectly definite, of restricted scope, completely evolved, and accessible to research in all the phases of its development, from the lowest to the highest. It is that of _numeration_.