i82 THE INFANCY OF ANIMALS 



unlike out of matter which, by all human tests, is identical 

 is one of the greatest of all mysteries. 



In about a week this black sphere has become ovoid, 

 and by the tenth day slight constriction foreshadows the 

 development of a head, body and tail. Presently this 

 growing body assumes the form of a young fish, branching 

 tufts growing out on each side of the head to serve as gills 

 or breathing organs. In about a fortnight from the time 

 the egg was laid, the tiny body wriggles its way out of its 

 jelly-like envelope and swims freely in the water. It has now 

 ceased to be an embryo, and has become a " larval " frog. 



But its swimming excursions soon cease, for almost atonce 

 it proceeds to attach itself to some piece of weed in the water 

 by means of a pair of sucker-like organs on the under surface 

 of the head. Here for a few days it hangs motionless, waiting 

 for its mouth to grow, for as yet this very important orifice 

 is conspicuous by its absence, and the body is nourished by 

 whatremainsof the food yolk originally stored within the egg. 



The mouth makes its appearance a few days after 

 hatching ; and a wonderful mouth it is, bearing not the 

 remotest likeness to the mouth which will presently succeed 

 it. In the first place it is fringed by two large fleshy lips, 

 which, seen under the microscope, are found to bear rows 

 of horny, claw-like teeth, with serrated edges under the 

 curve of the claw. Altogether there are some 640 of such 

 teeth, and what is more, these are constantly being shed 

 and replaced, the new teeth lying one inside the other, so 

 that as the uppermost is shed the one hitherto lying within 

 it comes into use. Thus, during this brief period of larval 

 life it uses up a thousand or so of these teeth. They are used 

 chiefly for hooking on to the food, which is demolished by 

 the jaws. These are similarly armed with hundreds of tiny 

 teeth, so closely packed as to form a kind of beak, recalling 



