mammals though in the case of whales, whose nonconducting coats are of blubber, the hair is reduced to a few bristles on the lips. The advantages conferred by warm blood and superiority of brain are seen by the alertness and activity of mammals, who, in general, are not subject to the prolonged periods of stupor familiar in animals of lower organization. Increased powers of locomotion were given by elongation of the limbs, shortening of the tail, and development of muscles. Some mammals, as the present-day kangaroos, lemurs, monkeys, and apes, achieved a mode of progression by which the fore-limbs were more or less set free for grasping. In man, and man alone, the arms have been completely released from the support of the body, and so the craftsman's skill has become possible. Bats are the only true flyers in the group. 'Flying' squirrels do not really fly. When they jump from branch to branch they spread out a flat surface on each side of the body which, acting as a parachute, carries them through the air for some distance without falling. Whales have evolved another mode of locomotion, but are in all probability descended from land-dwelling ancestors. Their enormous bulk-- they include the hugest creatures that ever existed, the eighty-five-feet-long rorquals, surpassing in size even the great reptile dinosaurs would be evolved after they had adopted a water life, where weight would no longer have to be supported by muscle. Though high organization of structure is as a rule accompanied by large size, and the mammals are in general larger than the other backboned animals, a stage is reached fairly soon in land animals when further increase of bulk with its accompanying cumbrousness and conspicuousness is a drawback rather than an advantage. Thus

we find that among mammals the water-dwellers are the largest, land animals come next, and last the tree-dwellers and 'flying' mammals, which, to maintain their equilibrium when moving, need enormous muscular power in proportion to bulk.

Thus, with powers of locomotion inferior only to those of birds, and like birds able to conserve an internal warmth which enables them to endure great variations of temperature, the mammals have spread over most of the earth's surface, from regions of Arctic cold to those of tropical heat. The number of existing mammal species is, however, less than that of either birds or reptiles; it is less than it has been in earlier epochs, so that from the point of view of variety it may be said that the culminating point of the mammal group is past. As the beginning of this decline appears to coincide with the appearance of man it is at least probable that man contributed to it. At the present day his supremacy is such that he exercises a great controlling influence on the whole animal world. Because the usefulness of mammals to man is greater than that of the other animals their natural predominance is backed by their economic value. More and more in the future the fittest' may be chosen from a human standpoint, and man may supplant nature in selecting those species which he wishes to survive. It does not follow that the power of selection would be used wisely. Cruelty and greed have resulted, for instance, in the extinction of the king bird of paradise, the most beautiful of living things. Human interference with the design of nature might conceivably lead to the downfall of man.

The origin of the mammals, as has been mentioned, has been traced with considerable probability to the

theromorph branch of the great reptiles. These show signs in all parts of their skeletons of evolution along mammal lines, and in the particular species from which mammals are believed to have been derived there is a marked resemblance to the higher group in the skull and teeth. Instead of sprawling like the typical reptile they carried their bodies clear of the ground on legs of fair length, the segments of which had the relative position characteristic of mammals. In general the size of the theromorphs appears to have been that of a wolf or a bear, so that the earliest mammals showed a degeneration in this respect from their ancestors, or, as is more probable, sprang from A CRESTED THEROMORPH Co-existing smaller types. The oldest mammal remains known to us consist of teeth and very small lower jaw bones found embedded in firm-textured rock. These jaws are seldom as much as an inch in length, and appear to have belonged to small opossum-like creatures about the size of a rat. A few such remains were discovered about eighty years ago in the Stonesfield slates near Oxford. Mammals, though the latest evolved animal group, are shown by their fossil remains to be of exceedingly ancient origin, but the earliest types are all extinct, and it is not till the close of the chalk epoch and the opening of the present era of the earth's history that we have any evidence of the existence of the ancestors of the modern mammal

PROBABLE APPEARANCE OF

species. Early in this epoch we find most of the existing orders, as well as some that have now disappeared. The number of types goes on increasing to the middle of the epoch, when a gradual decline in variety sets in, and this diminution of species has continued to the present day, as instanced by the recent disappearance of the quagga, and the lessening numbers of the American bison and white rhinoceros. From the early stock of small mammals there appear to have been two offshoots, one showing a specialization of structure that left the brain undeveloped, and which consequently died out entirely-unless the pouched animals of Australia are its representatives, surviving because the fact that Australia was early cut off from communication with the rest of the world preserved them from the competition of animals with developing brains -the other branch giving rise to the species which exist to-day. It is believed that the ancestors of all the mammals were little tree-dwellers with small heads and long tails, living in swampy forests. Most of their descendants deserted the forests for the plains, and brain-growth was accompanied in them by changes in the body which resulted in such different types as horses, cattle, deer, camels, and lions. Others remained in their original homes, and little essential change took place in them except the all-important development of brain.

It is often supposed that the animals of to-day are puny descendants of giant predecessors. That is not So. As has been seen, the earliest mammals were all small, and a gradual increase in size seems to have taken place, in some cases producing huge forms in which bulk was disproportionate to brain, and which were doomed to extinction. A study of the descent of

rhinoceroses, camels, horses, and other existing orders of mammals makes clear the fact that the types of to-day have gradually evolved, in increase of size as in other respects, from smaller ones of the past. The great extinct beasts are often found to be not the true ancestors of any living types, but representatives of related ones, which disappeared and left no direct descendants. When a group of animals meets with adverse conditions, such as the pressure of new enemies, or changes of climate and scarcity of food, it is the large types, which are conspicuous and also require much food, which tend to disappear, while the small forms escape notice, need little to sustain them, and have a better chance of survival. Thus the small tree-sloths, armadillos, and ant-eaters of South America are the present-day representatives of small, perhaps smaller, ancestors which were contemporary with the giant sloths and armadillos which are now extinct. The latter were dominant as long as South America was an island, cut off from the evolution of the great mammals in North America, Europe, Africa, and Asia. But when South America became joined to North America, and received from her the mastodons, horses, tapirs, tigers, and other animals that had been produced during her own insular existence, the great forms succumbed to the pressure of their better organized rivals for the possession of the land, while the small forms were able to carry on their race.

Present-day horses are bigger than extinct horses, and much bigger than their three- and four-toed ancestors. The first undoubted horse-like animal, found in the rocks of North America, is not more than eleven inches in height. Present-day elephants are as big as any of their predecessors, and much bigger than