VERTEBRATA AMPHIBIA. 



47 



tents into the common ventricle, which drives this mixed 

 fluid partly through the system, and partly to the lungs. 

 The blood is cold. The red corpuscles are oval, and 

 contain a central nucleus. 



FIG. 16. METAMORPHOSIS OP TOAD. 



a, ova; &, tadpoles just hatched; &', tadpole enlarged to show external 

 gills; c, tadpole after losing external gills; d, the same after development 

 of posterior limbs ; e, provided with both pairs of limbs ; /, tail begins to dis- 

 appear; g, tail almost wholly absorbed. 



56. Covering. The covering consists of a soft moist 

 skin, which is generally destitute of scales. 



57. Development. The Amphibia all undergometamor- 

 phosis (Gr. meta, change; morphe, form). The eggs are 



