THE FROG 241 



of the egg. The rest of the egg is made up of food or yolk, 

 and when the baby fish hatches it has for some time the yolk 

 attached to its ventral surface. Eventually the food is absorbed 

 into the body of the fish. The development of the fish is direct, 

 the young fish becoming an adult without any great change in 

 form. The young fry are kept under ideal conditions until later, 

 when they are shipped, sometimes thousands of miles, to their 

 new homes. 



Early development of salmon. Natural size. 



Note to Teacher. — It is suggested that in the spring term the frog be studied, 

 but if animal biology be taken up during the fall term the fish only might be used. 



THE FROG 



Adaptations for Life. — The most common frog in the eastern 

 part of the United States is the leopard frog. It is recognized by 

 its greenish brown body with dark spots, each spot being outlined 

 in a lighter-colored background. In spite of the apparent lack of 

 harmony with their surroundings, their color appears to give 

 almost perfect protection. In some species of frogs the color of 

 the skin changes with the surroundings of the frog, another means 

 of protection. 



Adaptations for life in the water are numerous. The ovoid 

 body, the head merging into the trunk, the slimy covering (for 

 the frog is provided, like the fish, with mucus cells in the skin), 

 and the powerful legs with webbed feet, are all evidences of the 

 life which the frog leads. 



Locomotion. — You will notice that the appendages have the 

 same general position on the body and same number of parts as 

 do your own (upper arm, forearm, and hand ; thigh, shank, and 

 foot, the latter much longer relatively than your own). Note that 

 while the hand has four fingers, the foot has five toes, the latter 

 connected by a web. In swimming the frog uses the stroke we 



HUNTER, CIV. BI. 16 



