142 ANURA 



the members of the same family. The fact is, that the Aiiura 

 are a very recent and a most adaptive, plastic group. The earliest 

 known fossils are scarcely older than the Middle Eocene. 



Almost every one of the greater families has produced terres- 

 trial, 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, denti- 

 tion, general shape of the body, length of limbs, wartiness of 

 the skin, tympanic disc). These are the so-called adaptive charac- 

 ters, 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 Eanidae, like Rhaco- 

 phorus, which by their green colour, large adhesive discs and 

 arboreal habits may well put any of the Hylidae 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 Cysti- 

 gnathidae 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 Eanidae being the 

 highest of all the Anura, and amongst them the Eaninae 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 natu- 



