The Dawn of Reason; or, Mental Traits in the Lower Animals

by Jr. James Weir

For a very long time I believed that this function was a distinct sense, and, five years ago, I set to work in search of the sense's centre. After many dissections I found it (in the frog) lying immediately below the optic centres and closely connected with them. Nerve-fibres of the sympathetic can easily be traced and can be seen to penetrate this centre. When this centre is artificially stimulated either with the point of a needle or with a mild electric current, tinctumutation can be incited at will.

Again, when this centre is destroyed (which can be done without injury to the optic centres), the chromatophoric function ceases—the phenomenon of tinctumutation is no longer observable.

That the sympathetic nerves are the carriers of the messages from the optic nerve and the color-changing centre, can be demonstrated by other means than by excision of the nerve. Atropine, to a certain extent, paralyzes the sympathetic when given in sufficiently large doses, and injections of this drug beneath the skin of a frog render the division of the sympathetic unnecessary. The chromatophores will not respond to light impressions if the animal be placed thoroughly under the influence of atropine.

A large number of the lower animals possess the chromatophoric function. Several years ago, I placed in a large cistern several specimens of gilt catfish. This is a pond fish and is quite abundant throughout the middle United States. It is of a beautiful golden yellow color on the belly and sides, shading into a lustrous greenish yellow on the back and head.

Several months after these fish had been placed in the cistern, it became necessary to clean the latter, and the fish were taken out. They were of a dusky drab color when first taken out, but soon regained their vivid tints when placed in a white vessel containing clear water. They had evidently changed color in order to harmonize with the black walls and bottom of the cistern.

Certain katydids are marked tinctumutants. I took one from the dark foliage of an elm and placed her on the lighter-colored leaves of a locust. She could be easily seen when first placed on the locust; in a few moments, however, she had faded to such an extent that she was barely noticeable.

The larvæ of certain moths, beetles, and butterflies also possess the chromatophoric function. The chromatophores in the larva of Vanessa are very numerous, and this grub is a remarkably successful tinctumutant; the same can be said of the larvæ of certain varieties of Pieris.

The power of changing color so as to resemble, in coloring, surrounding objects is evidently one of Nature's weapons of defence. In some animals it is developed in a wonderful manner. Wherever it is found it becomes to the animal possessing it a powerful means of defence by rendering it inconspicuous, and in some instances wholly unnoticeable.

After nine years of careful, systematic, and painstaking investigation, I am prepared to affirm that, besides the senses, sight, smell, taste, touch, hearing, and tinctumutation, certain animals have yet another sense, the sense of locality, or of direction, commonly called the "homing instinct." This remarkable function of the mind is not an instinct any more than the sense of sight or smell is an instinct, but is, on the contrary, a true sense; for I have demonstrated by actual experiment that it has a centre in the brains (ganglia) of some of the animals possessing it, just as the other senses have their centres. And, since this centre has been found in certain species, and that, too, in creatures very low in the scale of animal life, it is reasonable to infer that it is present in the brains (ganglia) of all those animals which evince the so-called "homing instinct."

In the process of civilization certain of the five senses in man become dull and blunted; thus, the sense of smell in the Tagals of the Philippine Islands is much more acute than it is in the civilized European, and what is true of the sense of smell is also true of the other senses, save that of touch, in all primitive peoples. This last sense seems to be much more acute in civilized man than it is in savages. This, for certain psychical reasons, unnecessary to detail here, is a necessary result of evolutionary growth and development.[102]