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University of California Publications in Zoology [Vol. 19 



which follows the period of depression on November 18, when a pro- 

 nounced mode is seen in the curve. After November 18 a short period 

 of depression is characterized by a. falling off in the number of cysts 

 found, but their number begins to increase again, and had reached 

 fifteen cysts when the last examination was made. The intervals 

 between the modes are 7%, 6, and 3 days, respectively. 



10 



i 



I 



s 



2 



S 



?■ 



25 26 27 28 29 30 31 1 



4 5 6 7 8 



Eat 12 

 Fig. 11 



9 10 11 12 13 14 15 16 17 18 19 20 21 



25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 



Eat 13 

 Fig. 12 



Eat 12. There are four cycles of encystment represented in the 

 graph which was made from the data of rat 12. The cysts were found 

 during two successive days in the first cycle October 27 to 29. A 

 period of depression then continued for seven days when no cysts 

 were found in the faeces. The cycle which followed was only one day 

 in length and only three cysts were counted in the examination of the 

 faeces. The third cycle is preceded by two days when no cysts were 

 found. The mode of the third cycle was reached on November 10 

 when three cysts were found in twenty fields. A couple of days when 

 the number of cysts decreased to one in twenty fields then ensued, to 



