480 G- N. CALKINS AND L. H. GREGORY 



5. SIZE VARIATIONS IN DIFFERENT PURE LINES FROM ONE 

 ANCESTRAL CONJUGANT 



The pure lines of Paramecium caudatum which we have been 

 working with have given an excellent opportunity for the study 

 of size variations in different lines from one ancestral cell. This 

 is especially true of the J series which has been more extensively 

 studied than any other set. The daily observation of individuals 

 in different lines of this series have shown clearly marked and 

 constant variations in size amongst them. Line 20 for example 

 is made up of individuals which always appear smaller than 

 those of any other line, while line 21 is always made up of rela- 

 tively enormous forms. 



In order to test the matter of size variations more accurately 

 two sets of measurements were taken at an interval of about six 

 weeks. The material was obtained at each period from rich cul- 

 tures which had been prepared for the monthly conjugation tests. 

 These cultures were seeded on March 6 and April 17 with material 

 from the permanent cultures of the 23 lines of the J series. For 

 each set of measurements random samples from top and bottom 

 of each rich culture were killed in Worcester's fluid four days 

 after the rich cultures were seeded, for example, on March 10 

 and April 21. Measurements were made immediately and with- 

 out removing the organisms from the killing fluid. For these 

 an ocular micrometer was used in which each division has the 

 value of 13.75 microns. The measurements were made by one 

 of us only, 100 individuals from each line being measured at the 

 first period and 50 from each line at the second. As there were 

 only four lines remaining in quadrant A the number of lines 

 measured was limited to 16, or 4 from each quadrant, the lines 

 being so chosen as to give material for correlation studies of pure 

 lines from later sister cells in the first two quadrants and from 

 earlier ancestral cells in the last two. Thus lines 1 and 7, 16 and 

 20, 17 and 41, are from sister cells in the 32-cell stage while 2 and 

 10, 13 and 15, 26 and 29, 28 and 30 came from sister cells in the 

 16-cell stage after conjugation. We are deeply indebted to Prof. 

 H. E. Crampton for assistance in working up the material accord- 

 ing to biometrical methods. 



