For instance, the pigeon in its wild state broods but twice a year, but when do-mesticated six, and sometimes even nine times. In the latter case, a single pair would in four years produce 14,762 descendants according to Stillingfleet, and according to Linnaeus, over 18,000. The astonishing fecundity of some of the animalcules has already been illustrated. The mammalia alone bring forth their young alive, the duration of gestation being as follows in the following species: elephant, 20 months and 18 days; rhinoceros, 9 months; horse, 11 months; ass, 12 months; cow, 9 months; reindeer, 8 months; buffalo, 12 months; sheep and goat, 5 months; foxes and wolves, 5 months; Greenland whale, about 10 months. - Obviously there must be a correspondence of the structure of an animal to its habits and functions. For example, a carnivorous animal must have great strength and powers of locomotion, enabling it to overtake, seize, and destroy its victim. It must therefore have largely developed muscles and strong bones, and the teeth and jawbones must be especially strong, and the former of a peculiar form for tearing animal tissues. Such an animal must also have an acute sense of smell and of hearing, and a corresponding structure of the organs of these two senses.

It is therefore not wonderful that Cuvier could construct an entire animal from having a few of its bones given, and that Agassiz has deduced the form and structure of a fossil fish from its scales alone. - What is nourishment to one animal may prove to be poison to another. Pallas states that hedgehogs eat abundantly of cantharides without inconvenience. The sphinx of a species of caterpillar feeds on the acrid and poisonous juice of the milk thistle (tythimalis), and a certain worm on the leaves of the tobacco plant. Bees feed on and obtain honey from the secretions of many poisonous plants; and a kind of buzzard devours the nux vomica. Most animals, however, confine themselves within certain definite limits so far as the sources of their nourishment are concerned. Even the hog, which is usually spoken of as omnivorous, may be mentioned in illustration. It has been found that the ox eats 270 and rejects 218 plants; the sheep, 387 and 141; the goat, 449 and 120; the horse, 202 and 212; while the hog eats but 72 and refuses 171. This animal, therefore, except in cases of necessity, evinces even a superior discrimination in the selection of its food.

Some animals never drink at all, drink not being required if the food contain a large amount of water, as is the case with the succulent plants. The gemsbok and the eland, two species of antelope, are thus adapted to the sandy deserts they inhabit. - The amount of food required by animals depends upon its quality and their activity. A far less bulk of animal than vegetable food is required; and the greater the activity, the greater is the waste of the tissues, and the more nourishment is needed to repair them. The intervals of fasting are therefore determined mainly by this circumstance. While birds are eating most of the time when not asleep, reptiles pass months in succession without food, in the mean time being in a dormant state. And those of the mammalia which hibernate (as the dormouse, hedgehog, marmot, etc.) also pass the entire winter with little or no food. The sloth also has been known to suspend itself on a pole for 40 days without taking food. But irregularity of supply of food must also be taken into account.

The griffin vulture will retain its vigor for five or six weeks without food; but when opportunity recurs it does not leave its repast for days, or so long as a morsel of flesh remains, so completely gorging itself that it is incapable of rising on the wing till it has ejected the contents of its crop. A total privation of food is longest endured without fatal consequences by animals manifesting the lowest vital energy. Fourteen persons, male and female, survived starvation on being shipwrecked for 23 days. An eagle lived 28 days, and several dogs 30 days without food. On the other hand, land tortoises have been kept alive 18 months and serpents for five years without food. The re-quirements of different animals in regard to their food will determine the limits on the globe within which each species will thrive; ! and this, together with the temperature required by each, is the principal agency deter-mining the geographical distribution of the ! various species of the animal kingdom. - The greatest amount of strength and endurance is possessed by the warm-blooded animals; birds ! being the strongest of all animals in proportion to their size, except certain insects.

The lion: is capable of bearing off large animals, and has been known to leap over a broad ditch with a ! heifer in his mouth, and to break the back of a horse with a single stroke of his paw. The grisly bear, weighing 800 lbs., can drag the carcass of a buffalo weighing 1,000 lbs. to a considerable distance. The camel sometimes carries a weight of 1,000 lbs. 30 miles a day, and judges so accurately of its powers that, being accustomed to lie down while loaded, it refuses to rise till a part has been taken off, if too heavy a burden is imposed. The horse is about six times as strong as a man, his power being estimated at 420 lbs. at a dead pull. He cannot, however, carry more than three times as much weight up a steep hill. A Canadian shrew mole, whose body was hut four inches long, being let loose in a room, passed between the legs of some heavy chairs and the wall with which they were in contact, throwing them aside without much apparent effort, and at last hid itself behind a pile of quarto books more than two feet high, which it also moved from the wall. This animal also burrows so quickly, that on being let loose in a yard it almost instantly disappears beneath the surface of the ground.

On the other hand, the sloth is so averse to all effort that, when it has satisfied its appetite upon the fruits of trees, it falls to the ground to save itself the labor of descending. - As instances of fleetness of animals, the kangaroo, the hare, and the antelope may be alluded to. The first progresses by a rapid series of leaps, frequently of 20 feet, its own body being from 5 to 0 feet in length. The hare sometimes passes over 25 feet at a single bound. The springbok bounds to the height of 10 to 12 feet, clearing at each leap from 12 to 15 feet without any apparent exertion. Even the sheep in its wild state runs and leaps with great agility. The movements of the dolphin are also very rapid, and it leaps so high: out of the water as sometimes to throw itself upon a ship's deck. The ostrich will at the outset outstrip the fleetest horse. The nandu (allied to the ostrich) is equally fleet, and when caught kicks so violently as to break even stones. The carrier pigeon flies 25 to 30 miles an hour.