HABITS OP TADPOLE. 165 



but little fringes at the sides of the neck." These fringes are 

 the Tadpole's breathing organs, and one of the earliest changes 

 it experiences is the shrinking of these organs, and their subse- 

 quent disappearance beneath the skin, where they discharge the 

 functions of the gills of a fish. The mouth of the Tadpole is 

 placed low down in the front of the head, so that when the little 

 fellow wishes to seize anything floating on the surface of the 

 watt., he has to throw himself on his back like a shark ; and so 

 nimbly does he execute this manoeuvre, that the eye cannot with- 

 out difficulty follow it. Thus expert in appropriating food, the 

 tadpole rapidly increases in size, the tail acquires greater breadth, 

 and the limbs slowly make their appearance. The hind feet are 

 developed first, increasing by little and little, and then the fore 

 feet also appear. The beak now falls off and exposes the true 

 jaws, whieh were before soft and concealed under the skin ; the 

 tail is gradually absorbed, and the young Frog begins to assume 

 something like his mature form. In a few days more the little 

 fellow, advanced to the dignity of positive froghood, takes his 

 leave of the water, and stops ashore, thenceforth repudiating the 

 shrivelled remnant of his once ample tail, which is now speedily 

 disposed of after the manner in which Lord Monboddo and his 

 disciples would have us believe that our own quadrumanous pro- 

 genitors disposed of theirs. 



While these external changes are in progress, modifications of 

 still more importance are taking place in the whole of the internal 

 organization. 



In the first place, let us look at the development of the spinal 

 column or back-bone. In the newly-hatched Tadpole this part 

 of the structure consists of little more than a simple fibro-cartila- 

 ginous cord. As the little creature grows, this cord begins to 

 ossify, though only in that portion which is to be retained in the 

 future Frog. After the process of ossification has gone on for a 

 short time, the cord becomes converted into a distinct vertebral 

 column ; both faces of the separate vertebra? in this early stage, 

 however, are concave, and between each pair of vertebra there is 

 precisely the same sort of hollow filled with fluid as that which 

 distinguishes the vertebral column of fishes. But ossification 

 proceeds ; and now gradually filling up the hinder cavity of each 

 vertebra, and projecting the newly-formed bone into the front 

 cavity of the vertebra behind, it finally converts the entire series 



