Utilities. Among both civilized and savage men Frogs are a culinary dainty. The edible European Frog is so much prized in France that it is bred for the market in large preserves. In the United States both the Bullfrog and spring Frog are sold in the markets. In France and the United States the hind legs alone are eaten; they are known as "saddles" to American marketmen, and are usually served at table fried. In Germany all the muscular parts are served stewed, often with sauce. Frogs have enabled man to contribute much to his knowledge of physiology. The tail of the tadpole, so frequently fed on by dragon-fly larvæ and other aquatic enemies, has great capacity of regeneration. The study of its re-formation has added to our knowledge of the regeneration of animal tissue. The circulation of the blood, so readily seen by the aid of the microscope in the web of the Frog's foot, is a classic and painless classroom demonstration. Observations on the response of Frog-muscle to stimuli led the great Italian physiologist Galvani to the discovery of dynamical or current electricity, known to us as galvanic or voltaic electricity.
Nests and Nest Building.
Whenever the spawning period occurs, ample warning will be given, as the male Frogs will begin croaking for their mate, and will be seen near the shore. Early in the spring is the breeding season, and the Frogs will be seen in pairs, working in company, selecting nests, which are in place where there is a vegetation to attach the spawn, near the surface of the water, as the action of the sun has much to do with the hatching of the spawn.
Impregnation takes place immediately after the spawn is deposited, as with the spawn of fish. The spawn of frogs looks like a gelatin mass in the shape of a bunch of grapes, and will be found attached to some vegetation in the pond. This should be immediately taken out with a large, long handle dipper and deposited in the hatching pond, as the spawn will be destroyed by the frogs jumping into the pond and coming in contact with it, for if the spawn is separated or broken up and sinks to the bottom of the pond, where it cannot get the proper action of the sun, many of the eggs will not hatch, but will be destroyed and eaten. The nursery, or hatching pond, should be constructed in this way: Make some skeleton frames that will set on the bottom of the pond, and come within a few inches of the top of the water. Fasten the frames down, either by weights or stakes driven in the ground. Take some fine netting such as used on windows to keep out flies; cotton or flax netting preferred to wire. Fasten this netting to the frame. Be sure that the netting is always covered with water when spawn is on it. On this netting, deposit the eggs or spawn taken from the breeding pond. In this way it will be undisturbed, and the sun can do its part toward the hatching of the eggs. This method will be found successful, and you can watch the progress, and the influence of the sun and water on the hatching of the eggs and note the change from day to day, as the Frogs have nothing more to do with their development. Another reason for separating the eggs or spawn from the breeding ponds is, when the spawn is hatched into tadpoles, the Frogs will eat the tadpoles as fast as they wiggle out of the egg. In fact, Frogs are cannibals, and will eat the young until they get large enough to protect themselves.
This is why ponds should be constructed so that Frogs of different sizes can be separated, and all of about a size, kept in ponds by themselves, and raised together. By this arrangement you save many small Frogs.
Enemies of Spawn, Tadpoles and Small Frogs.
The enemies must be guarded against by proper fencing with wire netting and boards. A board should be sunken into the ground at least three inches, and 2 foot 2 inch mesh wire fastened on it. If a 12-inch board is used, this will make a fence about 34 inches high. It could be built higher if desired, but this height makes a good appearance. The enemies are rats, cats, turtles, water centipedes, water beetles, coons, leeches and snakes. Snakes are one of the worst enemies, as they will devour the spawn, of which they are very fond, and also the small Frogs.