This weird creature is one of a decaying family whom naturalists, with needless and frank brutality, called toothless. The term is neither exact nor polite. It is very much as if one were to call a person “toothless” whose front teeth had been knocked out, but whose remaining teeth were good and useful. But it represents so important a taxonomic character that one must allow for what seems bad manners on the part of zoological leaders who are, as a rule, full of the milk of human kindness, and seldom in these days quarrel even among themselves, adopting the motto nihil animalium alienum a me puto.

Fig. 48.—Two-toed sloth, show­ing action of grav­ity upon the long thick hairs.

The sloths form an excellent example of the action of gravity upon long thick hairs, and the Fig. 48 given will explain this. They are New World animals, though indeed they have what we call an “Old World” look, and are truly ancient. They spend the larger part of their time upside down in the manner represented in the drawings. They are arboreal and nocturnal animals that come down to earth in search of food when things are quieter below, and will wander for considerable distances, walking slowly on the outer borders of their feet and the feet turned in.

These being the few facts of their lives which concern the present subject one comes, as usual, to interpreta­tion. These tree-sloths are descended from an older form that inhabited the ground, so that the present mode of life, which is so largely arboreal, has been acquired by dint of long years of struggle and adapta­tion to bitter needs. It seems hardly reasonable to call in the aid of selection for the produc­tion of its singular disposi­tion of hair though that factor ruled in the produc­tion of its arboreal habit. It is almost flying in the face of common sense to attribute this upward, or downward (according to one’s point of view) singular arrangement to anything but the effects of gravity upon its long hairs. If it be not so, it looks a remarkable likely solution of this small problem.

CHAPTER XV.
EXPERIMENTAL.

About ten years ago I began an investiga­tion into the results of the applica­tion by man to the domestic horse of various forms of harness, desiring to find out if these results were capable of being transmitted from one genera­tion to another. In 1908 I had not got very far, but thought it well to bring before the Zoological Society of London the results observed up to that time and read a paper entitled, “Some observations on the effects of Pressure upon the Direction of Hair in Mammals.” It was kindly received, but was not published in their proceedings, as it appeared to the Publica­tion Committee a paper more suited to “another place,” presumably those of a veterinary society. It was illustrated by the two figures I give here of a horse in full harness, and another with the chief results as to changes of the direction of hair, or new patterns, displayed on its coat.