Page:Popular Science Monthly Volume 33.djvu/807

This page has been validated.

relation to the environment. There can be little doubt that the enormous tusks of the early elephants and the formidable canines of many early carnivores would enable them at first to distance all competitors. But the law of acceleration tended blindly always in the same direction, till the old elephants seem to have been weighed down by their extravagant tusks, and the most highly specialized of all carnivores had canines so long that they could not shut their mouths, and both speedily became extinct. The law of retardation exhibits itself in the teeth of the higher races of mankind in a highly inconvenient manner. The greatly developed brain requires all the available room in the skull; there is no space left for the attachment of muscles for a powerful jaw. Cooked food also causes a degeneracy in the development of the jaw. There is constantly no room left for either the wisdom-teeth or the second upper incisors; the wisdom-teeth are retarded, often cause great pain, and decay early. The second incisors appear in startling and unexpected places, and often (in America especially) do not cut the gum at all. Prof. Cope says that "American dentists have observed that the third molar teeth (wisdom-teeth) are in natives of the United States very liable to imperfect growth or suppression, and to a degree entirely unknown among savage or even many civilized races." The same suppression has been observed in the outer pair of superior incisors. This is owing not only to a reduction in the size of the arches of the jaws, but to successively prolonged delay in the appearance of the teeth. In the same way men, and the man-like apes, have fewer teeth than the lower monkeys, and these again fewer than the insectivorous mammals to which they are most nearly allied. When this difference in dentition has been established, civilized man may claim to place himself in a new species, apart from low savages as well as from the high apes.



SPIDERS live in both hemispheres—from the torrid zone to the coldest regions. Over all the world they are distinguished by their singular aspects and curious habits. The largest and gayest-colored species are found in the tropics. In cold and temperate latitudes live smaller species and more tamely colored, which attract attention by other titles than that of their garb.

As classified by naturalists, the spiders compose an order of the class of Arachnida. They are the Araneids, a division so well characterized and perfectly circumscribed that it is suffi-