Chap, in.] AMPHIBIA. 93 



some can make overland journeys, and go up inclined 

 surfaces, if riot trees, like Anabas ; some can take 

 leaps out of the water, like the " flying gurnards " 

 (and the physostomous Exoccetus) ; some, like Chseto- 

 don, have a minute mouth, while the sword-fish has 

 its upper-jaw converted into a powerful piercing 

 organ, and another (Toxotes) has acquired the habit 

 of throwing a drop of water at the insect it desires to 

 obtain. Other examples might be given of the pro- 

 fusion of variation within the limits of Teleostean 

 organisation. 



Even the lowest of the Amphibia are dis- 

 tinguished from the highest of fishes, such as Cera- 

 todus or Lepidosiren, by the fact that their fore and 

 hind limbs are arranged on the same plan as in the 

 higher vertebrata (see page 350), and these limbs 

 terminate typically in five digits, so that, like the 

 higher forms, they are pentadactyle ; if, further, 

 fins are developed, they never have fin-rays. 



1. Urodela; in the lowest of these (Proteus, 

 Menobranchus) (Fig. 47) external gills persist through- 

 out life ; in the next grade (Amphiuma, Menopoma) 

 the gills are lost, but the gill-clefts remain ; while in. 

 the highest (Salamandra, Triton) the gills disappear 

 in the adults, and the clefts close up. All retain the 

 tail, which in the 



. 2. Aiiura (or frogs and toads) is only found 

 during the tadpole stage, when also respiration is 

 effected by external or internal gills, which disappear 

 in the adult, to be functionally replaced by lungs. 



3. Vsecilise are still more modified forms, in 

 which the limbs are lost, and the body is elongated 

 and serpentiform. 



The two higher divisions of the Vertebrata are 

 the Sauropsida and the Mammalia, which may 

 be grouped together as the Amniota* They are 

 characterised by the very early development of a 



