v THE DEVELOPMENT OF THE FROG 119 



back on the ventral side of the head, and gradually decrease 

 in size, and finally disappear. 



The hind limbs, which are the first ones to appear, bud 

 out as small papillae on either side of the base of the tail. 

 They gradually increase in size, become jointed in structure, 

 and later bud out the toes at the distal end. The fore 

 limbs develop in much the same manner ; the left limb 

 passes through the spiracle, the right one pushing through 

 the wall of the operculum. 



Toward the end of the larval period the tail begins to dis- 

 appear ; its tissues break down and are resorbed, serving, 

 doubtless, as food material for building up the other organs 

 of the body. During the transformation of the tadpole into 

 the young frog, the intestine shortens, the mouth becomes 

 much wider, and the horny jaws are shed, the tongue in- 

 creases greatly in size, the legs grow rapidly, the rounded 

 body changes in form, and the gills become resorbed ; the 

 lungs then develop rapidly, and the tadpole frequently comes 

 to the surface for air. 



The food of the tadpole is mainly vegetable matter. 

 Spirogyra and other algse are common articles of diet ; 

 animal food, however, is greatly relished. Tadpoles will 

 feed eagerly on decaying insects, earthworms, or almost any 

 kind of meat. They will also eat bread or fruits ; there are 

 few things, apparently, in the way of food, which they 

 disdain. 



REFERENCES 



The most complete accounts of the development of the frog are con- 

 tained in Morgan's book, "The Development of the Frog's Egg," and 

 Marshall's " Vertebrate Embryology." A more condensed account is to 

 be found in the small work on " The Frog," by the latter author. A 

 general elementary description of the development of the frog, based 

 mainly on the work of Marshall, is contained in Reese's "Introduction to 



