280 



ZOOLOGY 



Mouth. — Note the shape, position, and relatively large size of the mouth 

 in the frog as compared with man. 



Make a drawing of the frog in a natural position, having all parts visible 

 in the drawing carefully labeled. 



Characteristics of Amphibia. — The frog belongs to the class of ver- 

 tebrates known as the Amphibia. As the name indicates, members 

 of this group pass more or less of their life in the water, although in 

 the adult state they are provided with lungs. In the earlier stages 



of their development they 

 take ox3^gen into the blood 

 by means of gills. At all 

 times, but especially during 

 the w^inter, the skin serves 

 as a breathing organ. The 

 skin is soft and unprotected 

 by bony plates or scales. 

 The heart has three cham- 

 bers, namely, two auricles 

 and one ventricle. Most 

 amphibians undergo a com- 

 plete metamorphosis. 

 Life Habits of Green Frog. — The green frog inhabits shallow 

 fresh-water ponds, streams, and marshes. Much of the daytime 

 they may be seen sunning themselves. They live to a large extent 

 upon insects, which they catch by protruding their long bi-cleft 

 tongue. They also eat small algse and aquatic animals, and are 

 in fact omnivorous, even eating their own young. 



Life History. — During the first warm days in March or April, look for 

 gelatinous masses of frog's eggs attached to sticks or waterweed in shallow 

 ponds. Collect some and try to hatch them out in a shallow dish in the 

 window at home. Make experiments to learn whether temperature aff'ects 

 the development of the egg in any way. Place eggs in dishes of water in a 

 warm room and in a cold room, also some in the ice box. Make observa- 

 tions for several weeks as to rate of development of each lot of eggs. Also 

 try placing a large number of eggs in one dish, thus cutting down the supply 

 of available oxygen, and in another dish near by under the same conditions 

 of light and heat place a few eggs. Do both batches of eggs develop with 

 the same rapidity? In all these experiments be sure to use eggs from the 

 same egg mass, so as to insure all being of the same age. 



Development. — The eggs of the frog are laid in shallow water in 

 the early spring. Masses of several hundred are deposited at a 



Full-grown green frog, about half natural size. 

 Photographed by Overton. 



