Page:Popular Science Monthly Volume 46.djvu/402

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388
THE POPULAR SCIENCE MONTHLY.

upon children's actions to-day — an influence which can be easily discerned, though it may be sometimes obscured. Even such a matter as the elevation of the eyebrows during astonishment may be traced to the desire of prehuman ancestors to erect the hair, in order to make themselves as big as possible, and therefore formidable to their foes, a habit which animals constantly exhibit when they are suddenly startled. It is the noli-me-tangere principle, sometimes practiced with good cause, but at other times being the merest "bluff," a veritable trading under false pretenses. It is to this practice of erecting the hair that we owe the involuntary expression during extreme terror — that of the hair standing on end with fright. By disuse we have lost the voluntary power to control the muscles which perform the function of erecting the hair; but the involuntary power still remains. Such seems to be the explanation; at any rate involuntary erection of the hair during terror is a well-known fact, treated of by Darwin. Enough has been said to show that the characters and habits of children afford every support to the evolutionist; that what is quite unintelligible and even antagonistic to any idea of special creation becomes significant and full of meaning in the light of the doctrine of gradual development; that the actions of children when rightly interpreted tell their own tale and may fitly be compared to ancient monuments of prehistoric times; lastly, that the human infant is an interesting object of scientific research, and that even a cross baby should be calmly contemplated by the philosophic mind. — Nineteenth Century.


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ANIMAL TINCTUMUTANTS.

By Dr. JAMES WEIR, Jr.

THE chromatic function — and I use this term to designate the faculty of changing color according to surroundings — is possessed by a number of the lower animals. The chameleon is the best known of all the tinctumutants {tinctus, color, and mutare, to change), though many other animals possess this faculty in a very marked degree. In order to understand the manner in which these changes or modifications of color take place, one must know the anatomy of the skin, in which structure these phenomena have their origin. The frog is a tinctumutant, and a microscopic study of its skin will clearly demonstrate the structural and physiological changes that take place in the act of tinctumutation. The skin of a frog consists of two distinct layers. The epidermis or superficial layer is composed of pavement epithelium and cylindrical cells. The lower layer, or cutis, is made