_R. arvalis_ is often confounded with _R. temporaria_, as it differs from the latter only by the following characters. The snout is rather more pointed and is narrower; the inner metatarsal tubercle is large, compressed, and hard; the dorso-lateral glandular folds are more prominent and the belly is white and immaculate; lastly, it scarcely reaches 3 inches in length, a size which is not rarely surpassed by the other species. There are also some differences in habits. _R. arvalis_ prefers moist, boggy, open localities, and does not ascend beyond 2000 feet in Central Europe. It pairs as a rule later in the spring and the eggs are smaller, only 1½-2 mm. in diameter; they do not swell up so much, and the whole mass does not float but remains at the bottom of the shallow water. The coloration much resembles that of _R. temporaria_, and is likewise subject to much variation, except that the pale vertebral stripe is perhaps more common. This species is distributed over the whole of Central Europe, Russia, and Western Siberia, south of the 60th degree of latitude, living side by side with _R. temporaria_. Between the rivers Elbe and Rhine it becomes decidedly rare, and the latter river is practically its western boundary, while the Bavarian Alps and the Danube form its southern limits. _R. agilis_ is still more frequently confounded with both the two former species. It differs from either by the absence of the two internal vocal sacs of the male, and by the decidedly longer hind-limbs, the tibio-tarsal joint reaching often a little beyond the tip of the snout. The inner metatarsal tubercle is as prominent as in _R. arvalis_. Total length up to 3 inches. The prevailing colour of the upper parts is rather yellow or pink-brown with few and small blackish spots; a Λ-shaped dark mark on the neck is often present, and the large dark patch on the temporal regions is always conspicuous. The under parts are white, inclining to lemon yellow on the flanks and thighs. The iris is golden yellow in its upper half, dark brown in the lower half. {258}This species has a much smaller range than the first two:–from France through Middle and Southern Germany, Switzerland, and Lombardy to Hungary and Greece. The specific name refers to the quick and long leaps of this pretty, or rather delicately coloured frog, which prefers woods and wooded glens to large open places. Their voice differs much from the croak of the common Brown Frog, and agrees with that of _R. arvalis_, which is transcribed by Boulenger, who has kept them alive, as a rapidly uttered "co-co-co," or "cor-cor-cor." According to the same authority, the pairing takes place as in _R. temporaria_, but is of much shorter duration, the females usually resorting to the water only at night and when quite ready to spawn. Specimens in embrace are therefore seldom found in the daytime. The eggs resemble those of _R. temporaria_ in size, but they do not swell up so much and they do not float.