The child asks many questions, some of which are difficult to answer. Since what has been ascertained regarding the period during which the Tree-dwellers lived is not contained in books that are generally available, it has seemed best to present at this time such summarized statements as will furnish the teacher with the facts that she may need. ANIMAL LIFE _Extinct Species._ Among the animals of the mid-Pleistocene period that have since become extinct were the Irish deer; the big-nosed, the small-nosed, and the woolly rhinoceros; the mammoth; the cave-bear; and a sabre-toothed felis (_Machairodus latidens_), sometimes, though incorrectly, referred to as the cave-tiger. _The Rhinoceros._ The big-nosed and the small-nosed rhinoceros came to western Europe from the south. The former came the earlier and stayed until the late Pleistocene period, when the later cavemen hunted the reindeer. During this period it became extinct. As the climate became severe, both species may have migrated south each winter. It would have been possible, however, for them to remain, for they were well adapted to a cold climate. It is interesting to know that many of our popular tales of dragons originated in connection with the discoveries of the huge bones of these creatures, which could be accounted for in no other way. Our information regarding these creatures is exceedingly meager. They are characterized as dull-witted creatures with dim eyesight, exceedingly impulsive and dangerous. They rarely attacked other animals, for they lived upon vegetable food; but if they were molested they were formidable creatures. At such times they would root up young trees with their tusks, and pierce and rend the bodies of their most powerful assailants. A full grown rhinoceros was seldom attacked by even a mammoth or the sabre-toothed felis. Its thick skin served as an impervious shield, protecting it from the most powerful blows of the fiercest animals. It is quite probable that packs of hyenas and wolves learned to take advantage of precipices, and that they frightened the rhinoceros over the brink, thus disabling him so that he became an easy prey. The woolly rhinoceros came down from the north during mid-Pleistocene times and was protected from the cold by a fine inner coat which resembled wool, and a coarse hairy outer coat. This species was abundant until the close of the Pleistocene period, when it became extinct. What is stated above with reference to the characteristics of the rhinoceros applies equally well to this species. Very little has been written concerning these extinct species that is satisfactory for the teacher's use. Brief accounts can be found in Hutchinson's _Extinct Monsters_, p. 225; in Stanley Waterloo's _The Story of Ab_, p. 71; and in an article by E. D. Cope on "Extinct American Rhinoceroses," in _The American Naturalist_, Vol. XIII., 771a.