AMPHIBIA. 



Metamorphosis after birth, respiration branchial in 

 young', pulmonary, or pulmonary and branchial in the 

 adult, but always feeble in the lungs while active from 

 the skin ; lungs with few cells ; blood cold ; corpuscles 

 oval nucleated; circulation incomplete; heart in adult 

 with two auricles and a ventricle ;f reproduction ovipa- 

 rous or ovoviviparous ; foetus anamniate ; allantois want- 

 ing, unless the urinary bladder represents it ; skin usual- 

 ly naked or unarmed; skeleton incomplete, internal ; cra- 

 nium with two occipital condyles ; nasal sacs and pharynx 

 connected; nervous system cerebro-spinal ; brain small; 

 cerebellum scarcely visible; excrementitious and repro- 

 ductive organs opening into a cloaca. 



Exclusive of the extinct order Labyrinthodontia, none 

 of which have existed since the Trias, and which is char- 

 acterized by the labyrinthine teeth, the salamandroid or 

 rarely serpentiform body, and the presence of exoskel- 



*For anatomy see 5, 89 b, and 61. 



fA question has been raised as to the structure of the heart 

 in the Perennibranchiata. Proteus, and also the Axolotl in all 

 probability have only a single auricle. 



