1 68 



AMPHIBIA 



and are confined to the tropical regions of South America, 

 Africa and India ; none are found in Madagascar or Australia. 

 The tail is very short. The skull differs considerably from 

 that of other existing Amphibia and shows resemblances to that 

 of the extinct Stegocephali or Labyrinthodonts. The bones 

 are much broader and more solid than in other Amphibia, the 

 whole skull being firm and compact. The vertebrae are very 

 numerous, in some species more than 200 ; there is no trace of 

 the skeleton of the limbs or limb-girdles, or sternum. Most of 

 the vertebrae carry rather long ribs, which do not meet ven- 

 trally. The eyes are reduced to mere vestiges, and function- 

 less, either concealed under the skin or even beneath the 

 jaw-bones. The sensory organs which compensate for the 

 want of eyes are the facial tentacles, each of which is flat or 

 globular, not long, and is attached to the base of a pit between 

 the eye and the nostril ; it is protruded by being distended with 

 blood, like an erectile organ, and is retracted by a strong muscle. 

 There is a large gland whose secretion is discharged into the 

 sac of the tentacle. In many genera, but not all, the skin con- 

 tains calcified scales. The epidermis is continuous, but the 

 deeper-lying derma is in two layers bound together by trans- 

 verse lamellae in successive annular lines ; each compartment so 

 formed contains glands anteriorly and scales posteriorly. 



The following table shows the relations of the principal 

 divisions of the existing Amphibia : — 



Classification of Existing Amphibia. 



