86 



CLASSIFICATION OP AMPHIBIANS. 



4. AbrancJda has the genera Menopoma and Am} hi' 

 uma ; while 5. contains the singular genus Concilia. It 

 is easy to perceive that this last passes into the first by 

 means of the dipod sirens^ and thus the whole form a 

 circular group more or less perfect in its connecting 

 links. 



(92.) If .we look to those groups of the amphibians in 

 the foregoing arrangements which exhibit the most per- 

 fect metamorphosis, or, in other words, the highest de- 

 velopement of these characters which separate this class 

 from the true reptiles, we find they are exemplified in 

 the frogs and salamanders ; for, although the first ol 

 these never possess a tail in their adult state, while this, 

 member is permanently retained by the salamanders, 

 yet these are the only amphibians yet discovered, whose 

 respiration is totally different in their young and in their 

 perfect state. As tadpoles, they live in water, and 

 breatlie by external branchia ; but, when matured, they 

 respire atmospheric air and breathe by cellular lungs. 

 There can be no doubt therefore, that these two groups 

 follow each other ; and we are strongly inclined to be- 

 lieve, with Professor Bell, that they are the two typical 

 grcups of the whole class. In this case the three other 

 orders of his arrangement, viz. the Ahranchia, the 

 Amphipneurfa, and the Apoda, necessarily constitute the 

 aberrant divisions. 



(93.) The order Batracia {Anoura B.) contams the 

 wliole of the frogs and toads. To describe the form of 

 animals so familiar to every one will be unnecessary. 

 One of their most striking peculiarities consists in their 

 progressive motion upon land, being effected by leaping ; 

 Avhile the frogs, from the length and shape of their feet, 

 are also able to swim with great alacrity. Their meta- 

 morphoses are more perfect than that of the salaman- 

 ders, because the change of their form is much greater : 

 lience they may be considered the pre-eminent type of 

 the whole class. Their heart has but a single auricle 

 and ventricle, and they have two equal lungs : to these 



