i8 THE COMMON FROG. [chap. 



fore limbs are for a time concealed by the opercular 

 membrane. As the legs grow, the tail becomes 

 absorbed (Fig. 3, 7), not falling off, as some suppose. 

 The gills also disappear, and the branchial apertures 

 close, that on the right side first becoming obsolete 

 by adherence of the operculum to the skin of the 



body. 



As the gills diminish and cease to serve the pur- 

 poses of respiration, lungs at the same time become 

 developed in an inverse ratio, and the tadpoles ab- 

 solutely require to come to the surface to breathe. 



The process, from the hatching to the acquisition 

 of the miniature form of the adult, may be accele- 

 rated or retarded by elevation or depression of the 

 temperature. The Frog more than doubles its bulk 

 in its first summer.^ The young tadpole has at 

 first a very small mouth placed beneath the head 

 and not at its anterior termination ; it' is also for 

 a time provided with a sort of beak formed of two 

 little horny jaws. 



The food of the tadpole, quite unlike that of the 

 adult, consists largely (especially in its earlier stages) 

 of vegetable substances. 



Having now made acquaintance with the Frog 

 considered absolutely, or by itself, and also clearly 

 seen that it is a member of the Vertebrate Sub- 

 kingdom, we may enumerate the principal primary 

 subdivisions (Classes) of that sub-kingdom, and enu- 

 merate such of the next smaller groups (Orders) 

 as more or less nearly concern the subject of this 

 work — the Frog. 



1 Parker, Phil. Trans. 187 1, p. 172. 



