FROGS AND TOADS, 



277 



esting spectacle. The blood, forced from the heart in 

 regular pulsations, is seen to diverge into each of the main 

 gill-stems, sending off lateral streams to every tiny branch- 

 let : the red globules are seen to chase each other along 

 the tortuous vessels, to pass to the extremity of eveiy 

 ramification, and then, turning, follow a backward course, 

 until they reach the heart, the fountain from whence they 

 issued. 



But now these organs begin to disappear : they gradu- 

 ally diminish, until at length they can no longer be dis- 

 cerned externally, though their function is carried on in a 

 cavity of the body on each side. The little animal increases 

 rapidly in size, but does not change this its fish-like form 

 for a considerable period, though minor modifications may 

 be traced. Thus the mouth becomes developed, the eyes 

 are perfectly formed, and the tail-fin grows greatly in 

 perpendicular breadth, and is a powerful organ of locomo- 

 tion. The little Tadpole begins greedily to devour vege- 

 table matter, and manifests the effect of this diet in the 

 change of its own hue from a dull black to a soft olive- 

 green, with golden specks on the under parts. 



At length the period approaches when the Tadpole must 

 leave its aquatic life, and become terrestrial ; — at least it 

 must cease to respire water, and must derive its vitality 

 from the air. The first step to such a change, is the de- 

 velopment of limbs. First appear the hind-legs, in the 

 form of a pair of minute budding warts, which lengthen, 

 become bent, and shoot forth tiny toes at the extremity. 

 The fore-legs, always a little later than the hind, accom- 

 pany the latter in their gradual progress. As the new 

 organs of motion are acquired, the old one — the vibrating 



