[Pl. 101.]][M 161.
Edible Frog.
Rana esculenta.

[View Larger Image Here.]

Mr. E. S. Goodrich, F.R.S., has recently demonstrated that eggs obtained from a female Frog by dissection can be fertilised by the leucocytes or colourless corpuscles of the blood. He exhibited a fatherless Frog, so obtained, before the Linnean Society in November, 1918.

When all the tadpoles have become real little Frogs, with their legs sufficiently firm to enable them to indulge in hopping exercises, they still for a time venture no further than the very shallow water at the extreme edge of the pond, where they can walk partially submerged. Then one day there comes a heavy summer rain storm—a deluge on a small scale. Every little Frog then appears to hear the word "Go!" for with one impulse they all scramble out of the pond into the jungle of wet grass, they know not whither. If there is a road near, that is the place in which to form an idea of their prodigious numbers. The few wayfarers who may be hurrying along that road, looking for possible shelter from the pitiless rain, and seeing the Frogs hopping along much as the raindrops bounce, are quite prepared to declare that they came down from the clouds with the rain. Many persons who in the ordinary affairs of life would be regarded as reliable witnesses have testified that this is what happens. To them it seems a much more reasonable explanation of this sudden appearance—they term it a phenomenon—than the naturalist's statement that the Frogs had been waiting in the pond for the psychical moment to arrive for their dispersion—the time when the reeking herbage of many acres around would offer the safest conditions for their tender bodies to embark on the great adventure of life, their distribution over wide areas where they could carry out their proper function, the control of any inordinate increase in the insect population. For months they will crawl and hop invisibly among the lush grass and journey through the dense herbage of hedgebottoms and spinneys. Some will come under fences even into our gardens, to help us in an unequal warfare in which the gardener is always defeated by the insect, whether the bigger combatant admits it or not. Their food consists entirely of insects, slugs, and worms. In turn the Frog constitutes the food of many larger animals, including fishes, birds, snakes and weasels. The winter is spent embedded in mud at the pond-bottom, or in damp holes in the earth.

The Common Frog is distributed widely all over Britain, but is only of local occurrence in Ireland. Abroad it ranges over Central and Northern Europe as far as Sweden and Norway, and eastward to Mid-Asia.

Edible Frog (Rana esculenta, Linn.).

Although the Common Frog is the only species that is really native in Britain, another one—the Edible Frog, a Continental species—has been naturalised in the Eastern Counties of England since the early part of the nineteenth century, when Mr. Geo. Berney brought about 1500 specimens from France and Belgium and turned them loose in the Fens, in the neighbourhood of Stoke Ferry, where they are no longer plentiful, though they occur locally in various parts of Norfolk. A few years later (1843) Mr. Thurnall discovered the species in the Cambridgeshire Fens at Foulmire—a great distance (30 to 40 miles) from Stoke Ferry. Bell says his father had noted the presence of these Foulmire frogs, under the name of "Whaddon Organs," about the middle of the eighteenth century; so that it appeared that Mr. Berney had "taken coals to Newcastle"—in other words, had introduced the Edible Frog to a part of England where it already existed. In 1884 Dr. G.A. Boulenger discovered that the Foulmire frogs were of the Italian form of Rana esculenta known as the variety lessonæ, which made it doubtful whether they could be travelled descendants of Mr. Berney's frogs. So it was suggested that they were a survival from an introduction by the Romans—who are always dragged in to help out doubtful cases.

The difference in the French and Italian forms is mainly one of colour, the type being a beautiful grass-green, whereas lessonæ is olive-brown. But it has since transpired that lessonæ is not restricted to Italy as Boulenger thought, for he has more recently discovered it in Belgium and near Paris, and it has been recorded from parts of the former Austrian and German Empires. Such differences as there are in the two forms are not fundamental, and the brown tint of the Foulmire examples may be due to their environment. Fresh importations from the Continent have been liberated in recent years in Hampshire, Surrey, Oxfordshire, and Bedfordshire.

The Edible Frog attains to a rather larger size than the Common Frog. It is usually without the dark patch extending from the eye to the shoulder, and the markings of the body—especially the bright yellow and black marblings of the hinder parts—are darker and bolder. There is usually a light yellow or green line running down the middle of the back from the muzzle to the hinder extremity. The most distinctive feature, however, is restricted to the male sex: at the hinder angle of the mouth, just below the ear, are external vocal sacs which, when the owner is inclined to be melodious, become distended with air to the size of large peas, giving him a very quaint appearance. The croak differs from that of the Common Frog, and has been described as "more of a loud snore, exactly like that of the Barn Owl;" but this probably refers to the vocal efforts of the female, for Bell says it is so loud and shrill as to have obtained for the frogs the names of "Cambridgeshire Nightingales" and "Whaddon Organs." The males continue to "sing" after the breeding season is past, particularly on warm moonlight nights, when they may be heard for over a mile when the choir consists of several hundred voices. The notes are "Brekeke, gwarr, ooaar, coarx."