Ray observed the different tones used by the common hen, and found them uniformly significant of different ideas, or emotional states; therefore we may properly regard this as a system of language, though of a very rudimentary form. He distinguishes altogether nine or ten distinct tones, which are severally significant of as many distinct emotions and ideas—namely, brooding, leading forth the brood, finding food, alarm, seeking shelter, anger, pain, fear, joy or pride in having laid an egg. Houzeau, who independently observed this matter, says that the hen utters at least twelve significant sounds.[63] Many other cases could be given among Birds, and a still greater number among Mammals, of vocal tones being used as intentionally significant of states of feeling and of definite ideas; but to save space I will only render a few facts in a condensed form. “In Paraguay, the _Cebus azaræ_ when excited utters at least six distinct sounds, which excite in other monkeys similar emotions (Rengger).... It is a more remarkable fact that the dog, since being domesticated, has learned to bark in at least four or five distinct tones: ... the bark of eagerness, as in the chase; that of anger, as well as growling; the yelp, or howl of despair, when shut up; the baying at night; the bark of joy when starting on a walk with his master; and the very distinct one of demand or supplication, as when wishing for a door or window to be opened.”[64] I may next briefly add allusions to those instances of the use of signs by mammals which are fully detailed in _Animal Intelligence_. Mr. S. Goodbehere tells me of a pony which used to push back the inside bolt of a gate in its paddock, and neigh for an ass which was loose in the yard beyond; the ass would then come and push up the outside latch, thus opening the gate and releasing the pony (p. 333). With respect to gestures, Mrs. K. Addison wrote me of her jackdaw—which lived in a garden, and which she usually supplied with a bath—reminding her that she had forgotten to place the bath, by coming before her and going through the movements of ablution upon the ground (p. 316).