I62 VERTEBRATES 



study can be obtained at almost all times from April to De- 

 cember, and while the structure may be studied at any time, 

 it is desirable to study the development in the spring, when 

 the eggs may be easily obtained and observed in process of 

 change. There should be if possible at least three speci- 

 mens for each student and at the beginning of the study 

 one should be prepared for the study of the skeleton. If 

 the teacher has a microtome, much interest may be aroused 

 from the study of the egg in different stages of develop- 

 ment. Frogs may be kept for an indefinite period by feed- 

 ing them on small water animals. They are especially 

 fond of crayfish, but care must be observed to keep the 

 larger frogs separate from the smaller, as they do not hesi- 

 tate to eat a smaller one of their species. 



( I ) Where are frogs most abundant ? When danger ap- 

 proaches what protection do they seek ? Why ? Can a frog 

 remain under water for an indefinite period? Why? What 

 are its enemies on land ? Does it find enemies in water also ? 

 (2) Notice the covering. Is the frog moist after it has 

 been removed from the water for sometime? Is this an 

 advantage to the frog? Can you find out whether the 

 moisture comes from the body or the air? Study closely 

 the color of the dorsal covering. Is it the same in all frogs ? 

 External Morphology. — I. The Living Specimen.^- 

 Is it the same in the same frog at all times ? Can you think 

 of any advantage in the coloration as you see it now? De- 

 scribe the surrounding conditions suitable to the color of 

 the frog you have before you. If it changes describe the 

 probable cause for such change. Observe the color of the 

 lower surface. What apparent difference is there in the 

 colors of the upper and lower surfaces? Notice on the 



