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Page:Popular Science Monthly Volume 18.djvu/812

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THE POPULAR SCIENCE MONTHLY.

comes most quickly conscious of peril, and will outlive, as a rule, the one whose sensations have a longer distance to travel.

It can be easily shown that the mouth and the organs of taste and smell are as necessarily confined to the head, and that their special location is closely governed by that of the eyes.

For animals have safety of two kinds to provide for, safety from foes and safety from food; external and internal perils. Poisonous or unwholesome food is quite as necessary to be avoided as dangerous foes. The animal that is best protected against this peril has the best chance to survive. So important, indeed, is this necessity, that not alone the sight and the sense of touch and of temperature are on guard against injury from such a source, but two organs of sense, smell and taste, seem specially provided for this purpose alone.

The needful action of the eyes, as food-inspectors for the body, fixes the position of the mouth at such a distance from them that they will unavoidably perceive the food. Animals are not likely to voluntarily examine their food before eating it. They must be forced to do so involuntarily. Therefore, the eyes naturally command the entrance to the mouth, at the best distance for the most acute vision.

The relative positions of eyes and mouth being thus fixed, those of the smell and taste organs follow. Odorous emanations arise from the food significant of its character. The animal becoming most conscious of them has the best chance to escape danger. These odors naturally rise upward. The nose, as the organ of smell, is therefore best situated just above the mouth, and overhanging it, the performance of its function, as the organ of respiration, causing the respired air to sweep the lips and draw in the odors arising from the food.

The organ of taste, on the contrary, is best situated on the rear portion of the tongue, since the food must be masticated by the teeth, and partly dissolved by the saliva, ere it is in condition to excite the sense of taste. It must not be placed so far back, however, as to hinder the rejection of food warned against by the nerves of taste.

The head of the animal, then, seems necessarily to be just as we find it, the seat of the special senses and of the brain; while the relative location of these sense-organs and of the mouth, the position and elevation of the head, and the narrowness and flexibility of the neck, appear to be all necessary adaptations for the most complete protection of the whole organism.

The mammalian body, then, so far as we have yet seen, appears the best adapted of animal forms to gain extended and varied experiences of nature, to become exposed to diversified perils, and to evolve the most complete division of function. This body, once attained, is closely adhered to. While displaying thousands of minor variations, adapting it to special circumstances, it retains unvaryingly all the general characteristics mentioned. This close adherence seems to show that