510 



H. S. Jennings and George T. Hargitt. 



same date is given for different races, it will be understood that 

 those races had been kept for many generations under identical 

 conditions. This is particularly true for the last date given, April 

 21, 1910. In this case all the races measured had been kept, for 

 other purposes, under rigidly identical conditions, for a period of 

 seven weeks ; these measurements therefore probably give a very 

 correct idea of the relative sizes of the races. It has been thought 

 best to include in this table, for reference, the measurements of 

 most of the lines on which work was done, even though two lines 

 may belong to the same race, so far as size is concerned. 



TABLE 1 



Measurements of diverse pure lines of Paramecia at different dates. Each line 

 designated by a number or letter consists of the progeny of a single individual 

 (or in some cases of a single pair). The lengths given are the means of fifty to a 

 hundred individuals, and have a probable error in each case of less than two 

 microns. 



