THE FROG. 179 



The interesting habits of the frog should be studied in 

 the field if opportunity offers. 



Study of a Live Specimen. Study the live frog in the 

 laboratory. Observe : - 



1. The stocky, humpbacked body. 



2. The absence of tail and of fins. 



3. The presence of well-developed legs. 



4. The presence of eyelids. Touch the eye with a 

 pencil, and watch the lids. Are they of one sort? 



5. Its method of locomotion in water. 



6. Its method of locomotion on land. 



7. Its sitting posture. 



8. Its breathing : what external parts participate? 



Circulation of Blood. Wrap the frog in a wet towel, 

 leaving a hind foot protruding. Chloroform it, and ex- 

 amine with the microscope the circulation of blood in the 

 web of its foot, as directed for the fin of a catfish. 



Structure. Give additional chloroform, and, when the 

 frog is dead, study its structure. Note : 



1. The color and markings of the head and of the body ; 

 of the dorsal and ventral surfaces. 



2. The smooth, moist, scaleless skin. 



3. The prominent eyes, and behind them, on the sides 

 of the head, the round tympanic membranes of the ears. 



4. The wide mouth. 



5. A pair of nostrils above the mouth. 



Open the mouth and look into it. Observe : 



1. The fleshy lips which narrowly border the jaws. 



2. The absence of teeth from the lower jaw. 



3. The number, position, and arrangement of teeth in 

 the upper jaw. 



4. The long, fleshy tongue. Draw it forward, and find 

 the point of its attachment. 



