298 



AMPHIBIA 



day into a fish-like tadpole with distinct head, body and tail. Three 

 pairs o{ external gills ^ which are later to be replaced by internal gills, 



function i n respiration. I n 

 front of the two gill-arches 

 two depressions unite to form 

 a ventral horseshoe-shaped 

 sucker. Shortly after hatching 

 the mouth and anus are devel- 

 oped and the alimentary canal 

 becomes tubular and folded 

 while its diverticula^ the liver 

 and pancreas, are formed. 



Internal gills covered by 

 operculi replace the external 

 gills. Rapid increase in size 

 occurs, the tail which has been 

 developed to a remarkable ex- 

 tent soon begins to degenerate, 

 and the limbs appear. At 

 about the 8th week the gills are 

 replaced by lungs. At about 

 the loth week the tadpole 

 ceases to feed on algae, the 

 skin is moulted, the gills are 

 absorbed, the digestive system 

 assumes its adult condition and 

 the animal becomes carniv- 

 orous. Then the tail is com- 

 pletely resorbed, the hind limbs 

 Fig. 161 5. George M. Gray, Curator, ^ ^ ■' , , . , 



^.^ ■ D- 1 • t T u . elongate and the animal comes 



Marine Biological Laboratory. «.,njiiga.Lv, m, «_i 



(Photo by Chidester, 1931.) to shore as a young /ro^. 



References 



Hodge, C. F., and Dawson, J. Civic Biology. Ginn and Co. 

 Wright, A. H. 1910. The Anura of Ithaca, N. Y. A key to their eggs. 



Biol. Bull., vol. 18, no. 2, pp. 69-71. 

 Wright, A. H. 1914. Life Histories of the Anura of Ithaca, N. Y. 



Carnegie Inst. Washington, D. C, Pub. 197. 



