280 
H. S. JENNINGS 
DIFFERENT CONDITIONS FOR CONJUGATION IN DIFFERENT RACES 
Experimentation shows that the question, What conditions 
induce conjugation in Paramecium? is wrongly placed; it must 
be subdivided. The conditions for conjugation are different in 
different races. Experimenters on this matter will reach quite 
different results in differeat cases, depending upon what races 
are used. 
206 176 125 100 95 
Fig. 1 Diagram showing the relative average lengths of the diverse races of 
Paramecium used in the present work. The actual mean length of each race is 
given in microns below the corresponding outlines. The outline marked k shows 
approximately the mean size of the races g and C2 as well as of k. 
In my recent paper on Heredity, Variation and Evolution in 
Protozoa (1909), I have demonstrated the existence of many 
races in Paramecium^ differing constantly in average size. The 
relative sizes of a number of these races, including those with 
which T shall deal in the present paper, are shown in fig. 1. 
About ten different races or pure lines", each derived originally 
^ The work of the present and earlier, papers deals with the common infusoria 
that have been known under the name Paramecium aurelia, or P. caudatum, or 
under both names; to these belong the diverse races mentioned. 
