INTRODUCTION 191 



pair of orifices, the choancBj or inner openings of the 

 nostrils ; there is also in most Anura a pair of inner 

 ear-openings (Eustachian tubes). The tongue, which is 

 absent in a few of the tailless batrachians, may be more or 

 less completely adherent to the floor of the mouth, or 

 fixed only in front, or so constructed as to be protensible 

 to a very considerable distance, as in Chameleons. 

 The tail of the Urodeles is cylindrical in the land forms, 

 more or less compressed in those living in the water ; in 

 the European newts of the group known as Euproctus, the 

 organ is prehensile. In the Anura the tail is absent ; 

 in the Apoda it is also absent or extremely short. The 

 fore and hind limbs in the Urodeles are usually of 

 nearly equal length, while in the Anura the latter 

 are usually much the longer, and adapted for leaping ; 

 they are provided with four fingers and five toes in most 

 forms, although the digits may, as in some Urodeles, be 

 reduced to two only. The fingers are usually free, while 

 the toes are often provided with an extensive web. In 

 some Frogs both hand and foot are webbed to such an 

 extent that, as in the arboreal Bornean species of Rhaco- 

 phorus, they have been reported to serve as a parachute to 

 the creature when it leaps from branch to branch. Arboreal 

 species have the tips of the digits more or less strongly 

 dilated, and by means of these discs they are able to attach 

 themselves to smooth surfaces, as in the Geckos. The discs 

 do not act as suckers, as is generally believed, but adhere 

 by the intense pressure of certain muscles, supplemented 

 by a sticky secretion. The adhesion is not usually effected 

 entirely by the feet, but to some extent by the suctorial 

 action of the belly, which is developed to a certain extent 



