The bones of the fore-limbs of ordinary mammals are present in the cetacean flipper, but they become greatly flattened and overlaid with adipose tissue to form a paddle. In the right whales the five fingers of the mammalian hand are present, but in others one finger has been lost, and the digits are greatly elongated. The scapula, or shoulder blade, is a wide, flat, fan-shaped bone, and the clavicles, or collarbones, have entirely disappeared. The hind-limbs are rudimentary, when present at all, only being represented by bony nodules, and the pelvis is reduced to two spindle-shaped bones quite unlike that of land mammals. The skeleton of each group of the Cetacea, although similar in general characters, varies enormously in the details of construction, and to anyone interested in osteology will prove a fascinating subject for investigation. IV. ADAPTATION AS SHOWN BY THE CETACEA There are many indisputable evidences that whales once lived upon the land and walked upon four legs like ordinary quadrupeds, yet how remarkably different from any land mammal is their present form! We see that almost all aquatic creatures have torpedo-shaped bodies, which offer the minimum of resistance to their passage through the water. Thus as the whales gradually changed from a terrestrial to an aquatic life their bodies assumed the elongated form essential for successful existence in a liquid medium. Accompanying this change of bodily shape was the elimination of all unnecessary structures which offered resistance, and the whale’s smooth, soft, hairless skin was one of the results. But the hair of a land mammal acts as a non-conductor, preventing the heat of the blood from being absorbed by the air, and as the whale’s body became naked it was necessary to blanket it with some other protective covering; thus the layer of fat or blubber developed between the skin and the flesh. Fish and amphibians do not need a warm covering because their blood is cold and changes with the temperature of the medium in which they live. Besides giving warmth to a land mammal, hair acts as a protection for its tender skin; but since a whale lives in the water, where bruises or abrasions are unlikely, such protection is unnecessary. With the loss of hair the sweat and oil glands which are present in the skins of land mammals finally disappeared. When any creature becomes aquatic it must necessarily develop means for progression through the water, and thus the caudal portion of the whale’s body by degrees expanded into the wide, flat, boneless tail, or flukes. But instead of being vertical to the axis of the body like the tail of a fish, the whale’s flukes are horizontal, obviously to give the animal greater facility in rising to the surface to breathe.