Almost every one of the greater families has produced terrestrial, arboreal, aquatic, and burrowing forms. Their habits have modified, and are still shaping their various organs, first of course those by which the animals come first and most directly into contact with their surroundings (_e.g._ adhesive discs, dentition, general shape of the body, length of limbs, wartiness of the skin, tympanic disc). These are the so-called adaptive characters, sometimes decried as merely physiological; as if habits, use, and requirements did not likewise influence and ultimately model every other organ (_e.g._ tympanic cavity, Eustachian tubes, vertebrae, ribs, coccyx, pectoral arch, etc.). There are true Toads, Bufonidae, which are as smooth, wartless, slender-bodied and long-legged as the most typical of "Frogs"; true Ranidae, like _Rhacophorus_, which by their green colour, large adhesive discs and arboreal habits may well put many of the Hylidæ to shame. _Ceratohyla_ has developed the claw-shaped terminal phalanges which are otherwise typical of, and peculiar to, the Hylidae, but this genus reveals itself by various details as a close relation of the other Hemiphractinae; and these fall in with the Cystignathidae on the strength of their cylindrical, not dilated, sacral diapophyses. In sketching the phylogenetic tree of the families of the Anura we have to proceed with great caution. There is not much doubt about the Aglossa. They have retained some of the most primitive characters, but have by now been so much modified and specialised that they are to be looked upon as an early side-branch. Among the Phaneroglossa the Discoglossidae are with certainty the oldest, but are now scarce in genera and species, and much specialised. The Pelobatidae connect them with the Bufonidae. The Cystignathidae form a rather ill-defined assembly which points downwards to the Pelobatidae, upwards to the Hylidae. There is no divergence of opinion about the Ranidae being the highest of all the Anura, and amongst them the Raninae the most typical, the Dendrobatinae the most specialised. If we assume that moderately dilated sacral diapophyses represent a more primitive stage than cylindrical processes, we shall {143}naturally look to the Engystomatidae as the connecting link between the Ranidae and the Arcifera, through Bufonoid creatures still with teeth in both jaws. If, on the other hand, we take the dilatation to be a further development from more or less cylindrical processes, then the Ranidae can be considered as having sprung from Cystignathoid creatures, which have consolidated their pectoral arch into the firmisternal condition; and in this case the Firmisternia would not be a natural group, the Engystomatidae pointing, to the Bufonoid stock. This would, to a great extent, mean a reversion to Cope's idea.