TREE-FROGS. 24:5 



that every globule of blood is distinctly and beau- 

 tifully visible.* 



The branchial tufts now begin to diminish, 

 while the Tadpole increases in bulk, until at 

 length the limbs bud forth and assume their 

 form and toes, the hinder pair being developed 

 first. The tail is now gradually absorbed, the 

 absorption commencing at the tip and proceeding 

 towards the base until the last trace has disap- 

 peared. The gills are by this time so much 

 reduced as to be withdrawn beneath the skin, 

 and are no more visible ; the eyes and mouth 

 are fully formed ; the colour has changed to an 

 olive-green, spotted with yellow on the under 

 parts ; and, in short, the animal is no longer a 

 Tadpole, but a little Frog. 



The respiration is now carried on by means of 

 large cellular lungs ; but the action of breathing 

 is not performed as in most other Vertehrata, 

 by alternate contraction and dilatation of the 

 chest, for the Frog has no ribs, by the depression 

 of which to enlarge the thoracic cavity, — but by 

 the actual swallowing of the air, the element 

 being forced down the windpipe into the lungs, 

 by an action perfectly similar to that by which 

 food is forced down the gullet into the stomach. 



But there is another agent employed in the 

 respiration of these animals beside the lungs, 

 namely, the whole surface of the skin. Nume- 

 rous and careful experiments have proved that 

 the blood is purified, and the vital functions go 

 on for a considerable time, after all access of air 

 to the lungs has been cut off, and even (by an 

 experiment, the wicked cruelty of which we cannot 



* " British Reptiles" QQ. 



