DEVELOPEMENT OF THE BATRACHIA. 439 



porary organs, for they serve the purposes of 

 respiration only until the proper gills are formed, 

 and they then shrink and become obliterated. 

 The true gills, or branchiae, are contained within 

 the body, and are four in number on each side, 

 constructed on a plan very similar to those of 

 fishes. Retaining this aquatic constitution, the 

 tadpole rapidly increases in size and in activity 

 for several weeks. In the mean time the legs, of 

 which no trace was at first apparent, have 

 commenced their growth. The hind legs are the 

 first to make their appearance, showing their 

 embryo forms within the transparent coverings 

 of the hinder part of the trunk, just at the origin 

 of the tail. These are soon succeeded by the 

 fore legs, which exactly follow the hind legs in 

 all the stages of their developement, 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 inflexions of the tail, and 

 the irregular impulses given by the feet. This 

 interval is also employed by this amphibious 

 being, in acquiring the faculty of respiring at- 

 mospheric 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 received into its newly 



