DEVELOPMENT OF THE BATRACHIA. 305 



creases in size and in activity for several weeks. In the mean 

 time the legs, of which no trace was at first apparent, have 

 commenced tlicir o;rowlh. The hind ]e2;s are the first to 

 make their appearance, showing their emhryo forms with- 

 in the transparent coverings of the hinder part of the 

 trunk, just at the origin of the tail. These are soon suc- 

 ceeded by the four legs, which exactly follow the hind 

 legs, in all the stages of their development, until they 

 have acquired their due proportion to the size of the 

 trunk. The animal at this period wears a very ambiguous 

 appearance, partaking of the forms both of the frog and of 

 the lizard, and swimming both by the inflections of the tail, 

 and the irregular impulses given by the feet. This inter- 

 val is also employed by this amphibious being, in acquiring 

 the faculty of respiring atmospheric air. We observe it 

 rising every now and then to the surface, and cultivating its 

 acquaintance with that element, into which it is soon to be 

 raised; occasionally taking in a mouthful of air, which is re- 

 ceived into its newly developed lungs, and afterwards dis- 

 charging it in the form of a small bubble. AVhen the ne- 

 cessary internal changes are at length completed, prepara- 

 tions are made for getting rid of the tail, which is now a 

 useless member, and which, ceasing to be nourished, dimi- 

 nishes by degrees leaving only a short stump, which is soon 

 removed. The gills are by this time shrunk, and rapidly 

 disappear, their function being superseded hy the lungs, 

 which have been called into play; and the animal now 

 emerges from the water, and begins a new mode of existence, 

 having become a perfect frog, (Fig. 199.) It still, however, 

 retains it aquatic habits, and swims with great ease in the 

 water by means of its hind feet, which are very long and 

 muscular, and of which the toes are furnished with a broad 

 web, derived from a thin extension of the integuments. 



No less curious are the changes which take place in all the 

 other organs for the purpose of effecting the transformations 

 rendered necessary by this entire alteration in all the ex- 

 ternal circumstances of that animal, — this total reversal of 



Vol. I. ,39 



