FAM. 4. HYLIDAE (Tree-frogs).–The upper jaw–in _Amphignathodon_ the lower jaw also–and the vomers carry teeth; _Triprion_ and _Diaglena_ alone have teeth on the parasphenoid also, and the latter genus is further distinguished by possessing palatine teeth. The vertebrae are procoelous and have no ribs; the sacral diapophyses are dilated. The omo- and meta-sternum are cartilaginous, the latter forming a plate with scarcely any basal or style-shaped constriction. The terminal phalanges are invariably claw-shaped and swollen at the base, and carry a flattened, roundish, adhesive cushion. The tympanic disc is variable in appearance, being either free, or more or less hidden by the skin. The tongue is also variable in its shape and in the extent to which it can be protruded. {186}Most, if not all, Hylidae are climbers, and many lead an arboreal life, but it does not follow that all the "Tree-frogs" are green. Their distribution is very remarkable. To say that this family is cosmopolitan with the exception of the African region, is literally true, but very misleading. There are in all about 150 species, and of these 100 are Notogaean; one-half of the whole number, or 75, being Neotropical; 23 are Central American, 7 Antillean, and about 18 are found in North America. One species, _Hyla arborea_, extends over nearly the whole Palaearctic sub-region, and two closely allied forms occur in Northern India and Southern China. Consequently, with this exception of three closely allied species, the Hylidae are either American or Australian. We conclude that their original home was Notogaea, and that they have spread northwards through Central and into North America. The enormous moist and steamy forests of South America naturally suggest themselves as a paradise for tree-frogs, and it is in this country, especially in the Andesian and the adjoining Central American sub-regions, that the greatest diversity of generic and specific forms has been produced. It is all the more remarkable that similar forest-regions, like those of Borneo and other Malay islands, are absolutely devoid of Hylidae (while there are about a dozen species in Papuasia), whose place has however been taken for all practical purposes by correspondingly modified Ranidae, notably the genus _Rhacophorus_. Lastly, the fact that tropical evergreen forests of Africa and Madagascar possess no Hylidae, but are inhabited by several kinds of tree-climbing _Rhacophorus_, points with certainty to the conclusion that the origin of this large and flourishing family of Hylidae was not in Arctogaea. The versatility and the wide distribution of the Hylidae has naturally produced cases of convergent analogy, and the various species of one "genus" may be in reality a heterogeneous assembly. Such an instance is probably the genus _Hylella_, of which four species live in the Andesian and Central American provinces, while the two others occur in New Guinea and Australia.