TREE FROG. Many different groups of tailless Batrachians (see Frog) are adapted to arboreal life, which is indicated by expansions of the tips of the fingers and toes, adhesive disks which assist the animal in climbing on vertical smooth surfaces. These disks do not act as suckers, but adhere by rapid and intense pressure of the distal phalanx and special muscles upon the lower surface, which is also provided with numerous glands producing a viscous secretion.
The best-known tree frog is the little Hyla arborea of continental Europe, rainette of the French, Lauhfrosch of the Germans, often kept in glass cylinders provided with a ladder, which the frog is supposed to ascend or descend in prevision of the weather. But recent experiments conducted on scientific principles show that not much reliance can be placed on its prophecies. This frog is one of the smallest of European Batrachians, rarely reaching 2 in. in length; its upper parts are smooth and shiny, normally of a bright grass-green, which may change rapidly to yellow, brown, olive or black; some specimens, deprived of the yellow pigment which contributes to form the green colour, are sky-blue or turquoise blue; the lower parts are granulate and white.
The family Hylidae, of which the European tree frog is the type, is closely related to the Bufonidae or true roads, being distinguished from them by the presence of teeth in the upper jaw and by the clawlike shape of the terminal phalanx of the digits. It is a large family, represented by about three hundred species, two hundred and fifty of which belong to the genus Hyla, distributed over Europe, temperate Asia, North Africa, North and South America, Papua and Australia. Close allies of Hyla are the Nototrema of Central and South America, in which the female develops a dorsal broad pouch in which the young undergo part or the whole of their metamorphoses. The genus Phyllomedusa, also from Central and South America, are quadrumanous; the inner finger and the toe being opposable to the others. and the foot being very similar to the hand. These frogs deposit their spawn between the leaves of branches overhanging water, into which the tadpoles drop and spend their larval life.
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