CLASS AMPHIBIA. 



83 



trace its development till it assumes its adult cliaracters. 

 The eggs of the Frog are deposited in water in gelatinous 

 masses, and the young Frog on leaving the egg is known 

 as a Tadpole. In this stage of its existence (fig. ST, a) 



Fig. 37.— Development of tlie common Frog (Rana temporaria); a Tadpole, 

 viewed from above, showing the external gills (</); b Side view of a some- 

 what older specimen, showing the lish-like tail; c Older specimen, in 

 which the hind-legs have appeared; d Specimen in which all the limbs 

 are present, but the tail has not been wholly absorbed (after Bell). 



the animal resembles a little fish having a large rounded 

 head, a protuberant projecting belly, and a long com- 

 pressed tail (6). Its breathing-organs are at this period 

 genuine gills, two sets of wliich exist at first. One set of 

 gUls is external, and has the form of little filaments placed 

 on the side of the neck (fig. 37, a, g). These, however, 

 soon disappear, and the animal then breathes by means of 

 a series of internal gills, contained in a kind of chamber, 

 and protected by a flap of skin, which conceals them from 

 view. The water is admitted to these gills by the mouth, 

 and the respiration at this period is carried on essentially 

 in the manner which distinguishes the true Fishes. At 

 this period of its existence, also, the animal not only lives 

 exclusively in the water, but it feeds upon vegetable mat- 



