An important limitation to great size in an animal is, it must be remembered, often imposed by the nature of the animal's food. Ten individuals each weighing a hundredweight will more easily pick up and swallow the amount of food required to nourish ten hundredweight of the species than will one individual responsible for the whole bulk, provided that the food is scattered and not ready to the mouth in unlimited quantity. A creature which has unlimited forest or grass or seaweed as its food will be at no disadvantage owing to its size. But a carnivor or a fish-eater or one depending on special fruits and roots not offered to him by nature in mass has to search for, and sometimes to hunt, or at any rate to compete with others, for the scattered and elusive "bits" of food. So it is that we find that the fruit-eating apes are not very big, and that terrestrial carnivors are small, though powerful and swift, as compared with cattle, deer, and vegetarian beasts. Ten carnivors weighing each ten stone will with their ten mouths "pick up" more prey than one carnivor weighing a hundred stone and having only one mouth. Even the carnivorous Dinosaurs such as Megalosaurus and Tyrannosaurus were much smaller than the vegetarian Iguanodon, Diplodocus, Brontosaurus and Triceratops on which (or on the like of which) they preyed–just as a tiger is smaller than a buffalo, and a wolf smaller than a horse. It is owing to causes of this nature that the life of some animals, and consequently their growth, is limited in duration. Occasionally the common lobster lives to a great age, and grows to be more than 2 ft. long. But he is doomed by his size; the smaller lobsters "go quickly around" and get all the food (carrion of the sea), and the big fellow has to starve. The whale-bone whales, it is true, take animal food; but it occurs in the form of minute sea-slugs and shrimps, which fill the surface waters in countless millions over hundreds of miles of ocean. Hence the whales of this kind have only to swim along with their mouths open through an unlimited supply of luscious food. The size of terrestrial animals is also, it appears, definitely related to the natural water-supply. There are very few small quadrupeds in the interior of Africa. On account of frequent "drought," the mammals have often to run a hundred miles or more in search of water. Only animals as big as the larger antelopes and the zebra can cover the ground. The smaller kinds die (and have, in fact, died out in past ages) in these regions of sudden drought. [Illustration: The gigantic reptile Diplodocus on land.] FOOTNOTE: