Amphibia. 83 



Again in the fall study the frogs when they gather once more 

 along the banks. See if you can find any of them in the act of 

 diving into the mud. Mark carefully some of these places, and 

 watch to see if the frogs come out again. Some very slight cover- 

 ing of leaves or sediment may serve to show whether or not the 

 frog has come out. How deep do they go? Do they change 

 their depth or position during the winter? What is the tempera- 

 ture of the mud at this time? How cold does the mud at the 

 bottom of creeks and rivers become during the coldest part of 

 winter? Does it vary much during the winter? 



LABORATORY STUDY OF THE LIVE FROG. 



1. Put a live frog into a tub of water and study carefully its 

 mode of swimming and floating. 



2. Notice how the frog sits when at rest. Make drawings of 

 the live frog in the sitting posture. 



3. What has the frog in common with other animals that jump 

 well? 



4. Watch closely the frog's breathing, paying especial attention 

 to the throat, nostrils, and sides. 



5. Touch the eyeball with a pencil, and note what follows. 

 Note the motions of the eyelids. Note the color of the frog's 

 eyes. What is the shape of the pupil? 



6. Test the frog's sense of hearing. 



7. What does the frog eat, and how does it take its food ? 



8. Look for slight pulsations near the end of the backbone on 

 each side, near the anus. These are the beatings of the lymph- 

 hearts. 



9. Keep one frog in the light and another in the dark and com- 

 pare their -colors after an hour. Vary the color surroundings to 

 see whether they affect the color of a frog. 



EXTERNAL FEATURES OF THE FROG. 



Kill a frog by wrapping it in a towel or piece of cloth of any 

 kind, and moistening the latter with chloroform ; or put a tea- 



