VERTEBRATA : AMPHIBIA. 521 



is the case with the Urodela. Even after the first apperance 

 of the limbs, the tail is still retained as an instrument of pro- 

 gression ; but as the limbs become fully developed, the tail is 

 gradually absorbed (fig. 283, d\ until in the adult it has wholly 

 disappeared. 



The development of the Frog is thus a good illustration of 

 the general zoological law that the transient embryonic stages 

 of the higher members of any division of the animal kingdom 

 are often represented by the permanent condition of the lower 

 members of the same division. Thus the transitory condition 

 of the young Frog in its earliest stage, when the branchiae are 

 external, is permanently represented by the adult perenni- 

 branchiate Urodela, such as the Proteus or the Siren. The 

 final stage, again, when the gills have disappeared and the 

 limbs have been developed, but the tail has not been wholly 

 absorbed, is represented by the caducibranchiate Urodela, such 

 as the common Newt. In some of the Tree-frogs, however, 

 there appears to be no true metamorphosis. Thus in the larvae 

 of Hylodes the branchiae are absent or evanescent, the anterior 

 and posterior limbs are developed contemporaneously, and the 

 tail is absorbed within the first day after emergence from the egg. 



The order Anoura comprises a considerable number of 

 forms, but may be divided into the three principal sections of 

 the Pipidcz, Bufonidcz, and Ranida. In the Pipida, or Surinam 

 Toads, there are rarely teeth, and the mouth is destitute of a 

 tongue. A singular and hideous species (Pipa Americana) is 

 the best known, and it inhabits Brazil and Surinam. In this 

 curious Amphibian the eggs are placed by the male on the 

 back of the female, in the soft integument of which, in cell-like 

 cavities, the eggs are hatched and the young developed. The 

 larvae possess external branchiae, which are very early absorbed. 

 In the aberrant form Dactylethra, the upper jaw is furnished 

 with small teeth, and the three inner toes of the hind-feet are 

 furnished with nails, as is the case with no other Amphibian, 

 except Salamandra unguiculata amongst the Urodela. This 

 curious form is found at the Cape of Good Hope and in 

 Mozambique, and its larvae appear to be destitute of external 

 branchiae. 



In the Toads, or Bufonidce, a tongue is present, but the 

 jaws are not armed with teeth. The tongue agrees with that 

 of the Frogs in being fixed to the front of the mouth, whilst it 

 is free behind, so that it can be protruded for some distance 

 from the mouth. In one Toad only (Rhinophrynus) is there a 

 tongue which is free in front. The hind-limbs are not dispro- 

 portionately developed, whilst the toes are only imperfectly 



