_R. temporaria_ (the common European Brown Frog or Grass-frog).–The tympanum is distinct, two-thirds the diameter of the eye in size. The first finger is slightly longer than the second, which is shorter and weaker than the others, whilst the fourth is the longest. All the fingers are quite free. When the hind-limbs are laid forwards along the body, the ankle-joint reaches to a point between the eye and the tip of the snout. The five toes, which are about half webbed, increase in length from the first to the fourth, while the fifth is about equal to the third. The sole of the foot has a small, blunt, inner metatarsal tubercle; the outer one is scarcely visible. The skin is smooth, always moist, owing to the minute mucous glands; but a series of larger glands forms a pair of folds along the upper sides of the back; beginning behind the eyes they converge slightly beyond the shoulders, diverge a little in the sacral region, and converge again towards the vent. Another, much feebler, Λ-shaped ridge lies between the shoulders. The male has two internal vocal sacs, which, when in use, bulge out the skin of the throat beneath the angles of the mouth like a pair of globes. It is further distinguished from the female by the stronger muscles of the arms and by a pair of swollen pads on the inner side of the first finger. During the pairing {252}season these pads are enlarged into cushions covered with black horny rugosities. The iris is golden, with dark specks. The coloration is, generally speaking, brown above, with black-brown irregular spots, especially on the sides of the body, and with cross-bands on the legs. The under parts of the male are white or pale yellow, with a bluish tinge on the throat, while the female is more yellow instead of white, inclining to orange. In both sexes the under parts are mostly spotted with darker colours. A large dark-brown patch, extending from behind the eye over the tympanum towards the shoulder, is always present and has given this frog its specific name. Otherwise the coloration varies considerably; more or less according to the locality and nature of the surroundings, and to individual variation and temporary change of colour.