Besides in the coloration, it differs from _B. viridis_ in the following points. The little subarticular pads of the toe-joints are paired, not single, and the hind-limbs are decidedly shorter, so much so that this species cannot hop. But it runs well, like a mouse, generally in jerks, stopping every few seconds, and owing {182}to this habit it is called the "running toad" by the field-labourers of Cambridgeshire. The skin is smooth, but less so than in _B. viridis_, owing to the slightly more prominent warts; the parotoids are small; a similar pair of glands lies on the upper surface of the fore-arm and another on the calf. The tympanum is rather indistinct. The ground-colour of the upper parts is light brownish yellow, with a green tinge and scattered green spots; most specimens have a narrow yellow stripe along the vertebral line and over the head. The under parts are white, more or less speckled with black. The iris is greenish yellow and speckled. The male, which is of the same size as the female,–very large specimens reaching 3 inches in length,–has a large subgular vocal sac, and develops nuptial brushes on the first three fingers, but the first lacks the thickened pad of _B. viridis_. The yellow vertebral line is sometimes absent in specimens from the south of France and the Iberian Peninsula; and since these southerners are as a rule more handsomely marked, the green being more pronounced and arranged in larger patches, interspersed with red spots, they much resemble _B. viridis_. Boulenger, who has paid especial attention to this vertebral streak, which is a not uncommon design in various species of different families, has made the interesting observation that the streak has never been found in Danish and German specimens of _B. viridis_, where _B. calamita_ occurs also, while it is not uncommon in _B. viridis_ of Italy, South-Eastern Europe, Asia, and North Africa, where _B. calamita_ is not found. Lastly, he remarks that in Eastern Asia, where neither _B. viridis_ nor _B. calamita_ with such a line occurs, the same character is assumed by some specimens of _B. vulgaris_. The only conclusion we can draw from these facts is, that for some unknown reason the streak is a desirable, but not necessary, possession, but that it is not kept by two species in the same country, _B. viridis_ dropping it entirely where the typically streaked species, _B. calamita_, also occurs. The breeding season does not begin in England and Middle Europe until the end of April, in cold springs not before May, but it lasts for several months. The males, congregating in pools in great numbers, make a loud noise, each individual uttering a rattling note which lasts a few seconds, the repetition distending its bluish throat into the shape of a {183}globe as large as its head. As the note is taken up by all the other males, a continuous chorus is established, which on warm and still nights can be heard nearly a mile off.