THE TURTLE. 199 



mens should be obtained while the weather is yet warm 

 in autumn, and kept until needed. They may be kept 

 alive for an indefinite length of time, without food, dur- 

 ing cold weather. In the winter season they are normally 

 inactive, and if kept in a moist, cool place, will need no 

 looking after. 



Study of a Live Specimen. Study the turtle alive. 

 After treating it to a good washing to remove the mud, 

 take it into the laboratory, and study its locomotion : 



1. Its walking. Note the position of its legs with ref- 

 erence to the body, the distance between its lower sur- 

 face and the surface on which it walks, its rate of speed. 



2. Its swimming and diving. Place it in sufficient 

 water, and observe how its legs are used in these acts. 



Is its form well adapted for rapid locomotion of any sort ? 



Note how completely its head and appendages may be 

 retracted within the shell. 



Thrust a pencil toward the eye, and observe a thin, 

 transparent membrane come out from the inner u corner," 

 where it lies folded, sweep across the eyeball, and with- 

 draw again. This is the third eyelid (or nictitating mem- 

 brane). 



Respiration takes place very slowly, but occasionally the 

 animal may be seen to swallow a mouthful of air. 



External Features. Note among the external features 

 the following: 



1. The relative size of head and body. 



2. The hard shell or case which nearly incloses the 

 body. It consists of a convex dorsal plate, the carapace, 

 and a flat ventral plate, the plastron; and the two plates 

 are united by a bony bridge at either side. 



3. The color and markings of the wrinkled skin cover- 

 ing the neck and legs. Is any part of it scaly ? 



