Page:The American Cyclopædia (1879) Volume VII.djvu/517

 FROG 505 not for the storks of Egypt, that country would be overrun with frogs. When it is remembered that each female frog of the hundreds in a single locality may produce 1,000 young, which hide in crevices in the earth and under stones, ready to come forth to enjoy the genial summer showers, there is no necessity for any attempt to explain the appearance of the frog multitudes by supposing them to have fallen from the clouds, as has been believed even from the time of Aristotle, or by the supposition that they have been taken up from some marsh by a whirlwind and let fall during a rain ; the latter occurrence, on a small scale, is not impossible, in exceptional cases. The frogs which thus ap- pear bear marks of their recent metamorphosis, in the remnant of a tail and other organs ; crawl- ing as they naturally would into the ground, the swelling of the earth from rain would drive them out by compression. From facts recorded in the "Annals and Magazine of Natural His- tory" (1853, pp. 341 and 482), it would seem that frogs and toads may be reproduced without passing through the intermediate stage of tad- pole ; it is only of late years that many common fishes have been ascertained to be viviparous, and it is not improbable that eggs laid in local- ities where water cannot be obtained, as in cel- lars and hot houses and beds, may produce frogs, whose larval form is very soon exchanged for the perfect state, the gills being prematurely cast to enable the animal to accommodate itself to its new circumstances ; and it may be, as Mr. Jenyns remarks, that the frogs are hatched on land in the perfect state, the gills either never having existed or having disappeared imme- diately after birth. On the other hand, it "has been ascertained that the larval or tadpole state may be unnaturally prolonged ; Prof. J. Wyman (in the " Proceedings of the American Academy of Arts and Sciences," vol. iii., p. 35) experi- mented on the tadpoles of the common bullfrog, the greater number of which pass the winter without having undergone metamorphosis, not becoming perfect animals until the following spring ; he found that the tadpole state, by the influence of darkness and low temperature, could be prolonged certainly from one to two years, and probably much longer; possibly some of the cases referred to by Mr. Jenyns and others may admit of explanation by prolongation rather than an absence of the larval condition, the young frogs having been the result of tadpoles which had passed their larval condition in some other locality, or in the same in a torpid state for a year. The tenacity of life in frogs is very great ; they survive the severest wounds, live a long time after the heart and entrails are re- moved, and display muscular contractility and the phenomena of circulation in various organs for many minutes and even hours after death has actually taken place. On this account the frog has from time immemorial been selected as a subject of experiment to ascertain and illus- trate the most important phenomena of human physiology, and has in this way been of ines- timable advantage to mankind. The change of a fish-like animal, breathing by means of gills in water, to a leaping, air-breathing creature, with the corresponding modifications of food and habits, is well calculated to excite the admiration of a thinking person. The air cells of the frog's lungs, the membrane of its foot, and the delicate fringe of the tadpole's gills, afford admirable and easily obtained tissues for demonstrating under the microscope the circulation in the capillary vessels, with their chains of moving blood globules. The structure of the lungs and the mechanism of their respiration furnished to anatomists and physiologists proof of the changes which the blood undergoes under the influence of the oxygen of the air through the medium of a thin intervening vascular wall. The sensi- bility of their muscles to the galvanic currents led Galvani and Volte to most important dis- coveries in electricity and galvanism, whence flowed the great results obtained by Bell, Fara- day, and Matteucci in the physiology of the nervous system, and by Davy and others in physics and the chemical constitution of bodies previously supposed simple. The phenomena of cutaneous absorption, exhalation, and respi- ration have derived their fullest illustration and explanation from experiments made on the soft and naked skin of the frog. Thus this despised creature has rendered the greatest services to anatomy, physiology, physics, and chemistry, and has thrown light which no other animal coul'd on the functions of innervation, muscular contractility, circulation, respiration, absorp- tion, and generation. The frog is not only a graceful and harmless animal, but is actually use- ful in destroying insects and slugs injurious to vegetation. Though in England and the United States frogs are rarely eaten by man, in France and southern Europe they are largely consumed as food ; they are caught in various ways, and are preserved in large " froggeries " until want- ed for the table ; the flesh is most delicate and nutritious at the time when they are about to enter their winter quarters, yet great numbers are eaten in the spring, when they are more easily caught; the hind limbs are generally the only part eaten, and these are cooked in various modes, in all of which they are as much more delicate than chicken as that is superior to veal and pork. In the materia medica the flesh of frogs has long been used by continental physicians as the basis for anti-scorbutic and restorative broths. The largest species of the genus rana in the United States is the bullfrog (R. pipiens, Latr.), which often measures when extended 18 or 21 in. ; the general color above is green in front, dusky olive behind, with ir- regular black blotches, and below yellowish white, with dusky marks; the limbs dusky, with black bars. The bullfrog, so called from its loud voice, is rather solitary in its habits, living about stagnant and sluggish water, not very abundant in one place except during the breeding season ; it is the most aquatic of the frogs and an excellent swimmer, often living