448 Animal Biology 



spiracle. As the three pairs of external gills are resorbed, there are 

 formed four pairs of internal, fishlike gills (Fig. 222). In this stage the 

 suckers are small projections just behind the mouth. The mouth is sur- 

 rounded by a number of small projections known as the circumoral 

 papillae. The mouth also has a pair of horny jaws. The intestine shows 

 through the transparent ventral body wall as a long, coiled tube. This 

 great length of intestine suggests a typical vegetarian animal which the 

 tadpole really is at this stage. The hindlimb buds appear as small out- 

 growths on either side of the anal opening. These buds will continue to 

 grow by mitosis into the real hindlimbs. 



Fig. 221. — Metamorphosis of the frog (for previous stages, see Fig. 220). 1, 

 Tadpole just hatched; 2, 3, older tadpoles, side view; 4, 5, later stages, dorsal 

 views showing external gills; 6, tadpole with gills practically covered; 7, older 

 stage, right side showing hind limb; 8 and 10, later stages, lateral view showing 

 hind limb de\elopment; 9, tadpole dissected to show internal gills, spiral intestine, 

 and anterior legs developed within the operculum; 11, advanced tadpole just be- 

 fore metamorphosis; 12, 13, 14, stages in metamorphosis, showing gradual resorp- 

 tion of tail; 15, young frog after metamorphosis. (From Woodruff: Animal Biol- 

 ogy. By permission of The Macmillan Company, publishers.) 



