132 GARY N. CALKINS 



viduals would accumulate by division in the Syracuse dishes 

 during the first seven to eight days when food was plentiful. 

 With the transition from rich feeding to starvation, conjugation 

 should occur, provided the protoplasm is ready for it. During 

 this period of immaturity, however, no conjugations take place, 

 and at the end of two weeks the individuals are inactive and 

 greatly reduced in size through starvation. 



Conjugation tests made during the period of maturity give a 

 very different result. The individuals multiply as before during 

 the first week. Then they begin to collect in a single group 

 until a dense, white agglomeration is formed which sometimes 

 measures half an inch in diameter. Such agglomerations are 

 invariably followed by an epidemic of conjugations. Since each 

 conjugation test is started with a few individuals of the same 

 series that are left over after a daily isolation, the conjugations 

 that occur must be between closely related individuals of the 

 same age and with an identical previous history. 



In diagram 1 the ten-day averages given in table 2 are plotted 

 for the purpose of comparing the life cycles of the first eight series. 

 The ordinates represent the average numbers of divisions of a 

 single line in ten days. The abscissas represent the successive 

 ten-day periods. The positions of the curves in the first period 

 indicate the average division rate of each line during the first 

 ten days of life after conjugation, while the positions of the curves 

 in the tenth represent the average numbers of divisions between 

 the 90th and the 100th days after conjugation, etc. The period 

 during which conjugations occurred to furnish the filial series is 

 shown on the curve of the parental series by a letter which indi- 

 cates the filial series. Thus the points marked C, D, H, and J 

 on the curve of the A series indicate the periods when filial series 

 C, D, H, and J were started as ex-conjugants from pairs in the 

 A series. 



The successful and negative conjugation tests are shown in 

 diagram 1 by -f- and — signs, while the inconclusive tests due to 

 lack of material or to adverse conditions under which the tests 

 were made are indicated by question marks. The dotted line 

 connecting the first positive signs in different series indicates that 



