Slonaker, Activity of the Rat. 353 



out to the water boxes. This I think accounts for the occasional 

 short runs of often only a few revolutions of the cage. 



As the rats grow older, they become more and more like their 

 wild gray relatives in that they are almost wholly nocturnal in 

 their habits. They also become much more regular in their 

 periods of activity and rest. With the exception of a short period 

 of activity at the feeding time (8 a.m.) and an occasional short run 

 at other times during the day, they spend the entire day time withm 

 their nest boxes. They are presumably asleep during the greater 

 part of this interval. 



2 111 111 



3 4 5 6 7 8 9 10 II 12 i/VM. 234567s 



/une 25 



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4 III. HI II 



IP.M. 2 ,3 4 5 6 7 8 9 10 M 12 lA.M. 2345678 



June 26 



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Fig. 6. The graphic records representing the activity of each rat at the ages of 70, 71 and 72 days 

 as traced on the kymograph paper. The broken Hnes indicate periods of activity, the straight lines 

 periods of rest. 



The time in which they did the great bulk of their work varies 

 somewhat. In the winter time when the days were short they 

 began their running at an earlier hour. As the seasons changed 

 and the days became longer the time when they began their ac- 

 tivity gradually shifted to a later hour. In every case this time 

 appeared to coincide, in a general way, with the first deep shadows 

 of night. Earlier darkness caused by a storm or cloudy sky did 



