Belonging to the lower vertebrates is a family of animals called scientifically Ranidæ, but which are, popularly speaking, best known as frogs. They are queer-looking creatures, scarcely met with in Australia and South America, but reaching their highest state in the East Indies. They are capable of enduring great changes of heat and cold, and can live on land as well as in water, provided they have the amount of moisture necessary to preserve the suppleness of their skins. Salt water is fatal to the frog in any stage of its existence.
Rana clamata, the lusty croaker of the summer pond, is our most familiar species. He may be recognized by the colors of his dress, in which green, bronze, gold and silver play important parts, and by the ear-splitting character of his vocal intonations. The glandular ridges down the skin of his back, together with his strange coloration, singularly fit him for his home. Imitations of the stems of plants are seen in the darker ridges, and their leafage in the green color of his coat. The silver of his vest has the glimmer of the water in which he bathes, and the moist earth seems to have left its stain upon his brownish feet and markings, while the yellow of the several badges that adorn his person in being like the stamens and pistils of the surrounding flowers, and of the hue of many buds and blossoms, adds largely to his protective display. Thus is the frog in his natural haunts protected by his garments, and, unless he stirs or is betrayed by his full, bright eyes or the palpitation of his breast, he is not likely to be observed.
Four fingers or toes are found upon the anterior extremities, while those of the posterior are five in number and webbed. The front legs are much shorter, smaller and weaker than the hind ones, which are largely developed, and thus serviceable in swimming and leaping.
Though the frog is possessed of a back-bone, yet he has no ribs. Being ribless, he cannot expand and contract his chest in breathing, but must swallow what air he requires. In swallowing the air he must close the mouth and take the air in only by the nostrils; therefore, oddly enough, if his mouth is forcibly kept open, he will smother. The frog’s breathing, a fact not generally known, is partly through his skin, which gives off carbonic acid gas; and moisture, therefore, is just as essential to his skin as it is to the gills of a fish. Damp, rainy weather is his extreme delight. When the rain falls, out come the frogs. Their skin absorbs moisture, which is stored up in internal reservoirs, and some of this water, when these timid creatures are alarmed by being suddenly seized, is ejected, but I do not think that it is purposely so done, as the water is not, as some people have fancied, of a poisonous nature. Frogs have no poison-sacs, and in truth no weapons of any kind.
Open a frog’s mouth, and you will find but a few tiny teeth in the upper jaw and palate, which are useful for the partial grinding up of horny insects. His tongue you will discover to be a very odd affair, which is fastened at the front end of the mouth, the hinder part being free and hanging down the creature’s throat. This organ is covered with a glue-like secretion. When an insect is to be captured, it is snapped forward from the mouth, and, striking the insect, which it seldom fails to do, causes it to adhere as to bird-lime.
A few thoughts now about the life-history of the frog. From egg to egg is the story. In roundish masses, upon sticks lying in water, or upon the leaves and stems of submerged water-plants, are the eggs deposited. The creature that comes from the egg is no more like a frog than a caterpillar is like a butterfly. It has a large head, small tail, branched gills, and is devoid of limbs, resembling, in this stage, more a fish than a frog. This is its early childhood, or tadpole state. It can only live in water now, and swims and feeds from the very moment it leaves the egg. Change in form almost immediately begins, the branched gills being drawn within the neck and hidden, a pair of fore-legs beginning to bud, and subsequently a pair of hind-legs, which push out much faster than the fore-legs. As the legs grow, the tail is gradually absorbed and disappears. The interior of the body meanwhile changes, the lungs and heart becoming reptilian. When the gills and tail are gone, and the legs are fully formed, the once-swimming tadpole hops out of the water a perfectly-formed frog.
When first the tadpole emerged from the egg, it ate the jelly-like cover. Then soft animal and vegetable matters, with the strengthening of its pair of horny jaws, began to be devoured. Insects later on, and even its own kith and kin, became its food. The fare of the adult frog is almost exclusively insect in character, although necessity sometimes drives him to make a meal out of some of his weaker brethren.
Seated in cool, leafy shadows, not far from his favorite stream or pool, the frog watches with his great, black, gold-ringed eyes for such insects as good fortune shall bring to his retreat. As one hovers near, out flies his limber, sticky, ribbon-like tongue, true to its mark, and the hapless insect, adhering to the viscid projected ribbon, is gently and cleverly deposited in the open throat, the frog maintaining all the while an air of calm, superior self-satisfaction, as if he had not so much satisfied an appetite as fulfilled the mission of ridding nature of a superfluous insect.
A most harmless, timid and interesting animal is the frog, and often most unfortunate. He is the legitimate mark for all the missiles that can be thrown at him by urchins wandering about his native pool. Snakes make him their prey, and he is always in mental fear lest some insidious serpent shall take him unawares, or his musings shall be suddenly cut short by the stately progress of some swan or goose, sailing over the limpid water, or searching the green herbage wherein he sits concealed.
