OF THE COMMON FROG. 



463 



motion. After the 20th, the animals themselves 

 rarely remained under water above a few minutes 

 without coming to the surface, and carrying down 

 a small globule of air, and from this time they 

 swam with less rapidity and ease than formerly, 

 from the motion of the legs interfering with and 

 counteracting the action of the tail. On the 25th 

 of the same month, the fore-legs of several made 

 their appearance. With regard to these, I may 

 remark, that although the growth of the hinder ex- 

 tremities is exceedingly gradual, yet the fore-legs 

 make their appearance at once, nearly in a state of 

 perfection. Of this I discovered the reason, on a 

 more close examination. The growth of the an- 

 terior limbs is in fact internal, that is, they are con- 

 cealed in a hollow, under the lower jaw, near its 

 posterior angle ; and when the tadpole swims with 

 one side a little elevated, their motion, if carefully 

 observed, may be distinctly seen through the filmy 

 integument by which they are covered, some days 

 previous to their appearance externally. This I 

 had an opportunity of ascertaining, by means of 

 such as remained in a less advanced state. About 

 the 25th, also, the progress of ossification became 

 very visible, through the transparent skin of the 

 back. 



The body of the tadpole decreases in size, and 

 assumes the appearance of being emaciated before 

 the completion of all its limbs, at which time the 

 bony parts are easily discernible, froni the acute- 



