DECEMBER 1 28 



Like the fish, it breathes by means of gills and lives in 

 the water, but it has no fins and only one breathing hole, 

 which is on the left side of the body. 



From the gelatinous spawn of the frog is hatched out 

 a tiny fishlike creature Avith rudiments of gills and with 

 two disks on the head by which it clingi- to plants. Then 

 the three pairs of external gills develop. At their roots 

 are narrow clefts, which lead into the throat, out of which 

 conies the water taken in by the mouth. A fold of the 

 skin grows over the gills, leaving only a small opening 

 on the left side, through which they protrude for a time. 

 They soon atrophy, however, and are succeeded by in- 

 ternal gills. In the meantime, the eyes, the nose (two 

 nostrils in front of the eyes), the ears (circular patches 

 back of the eyes), become distinct. The tadpole eats 

 with a lip beset with numerous horny papillae surround- 

 ing the mouth. The intestine is very long and coiled like 

 a watch spring. 



The hind legs are first visible. With the growth of 

 the legs, the tail shortens, the mouth elongates, the lip 

 disappears, teeth develop in the upper jaw and on the roof 

 of the mouth, and the animal gives up its mixed diet, 

 preferring chiefly insects. 



The adult frog breathes by means of his skin, as well 

 as by his lungs. It is necessary for his lung respiration 

 that his mouth should be closed. The air is drawn in 

 through the nostrils, which then close, while the under 

 side of the throat is swollen, then flattened out, as the 

 air is expelled. 



There is a pair of lymph hearts, which may be ob- 

 served to pulsate near the end and on either side of the 

 back bone. 



The fore legs are much shorter than the hind legs. 



