194 



H. S. JENNINGS AND K. S. LASHLEY . 



not find it possible to measure a larger number. It appears hardly 

 probable that even so large a number will soon again be measured, 

 under the necessary conditions; moreover, the results reached 

 from the study of these 2687 specimens seem clear. 



Before proceeding to the study of these descendants of the pairs, 

 we must first examine the original wild culture, to determine what 

 the similarity is between the members of the pairs, owing to assor- 

 tative mating. Pearl ('07) and the senior author ('11 have 

 shown that there is a considerable degree of assortative mating 

 with respect to size, in Paramecium; larger specimens tend to 

 mate with larger; smaller with smaller. This tendency is meas- 

 ured by the coefficient of correlation in size for the two members, 

 a and 6, of the pairs. In the senior author's extensive study of 



TABLE 1 



Measurements in length of 180 non-conjugants taken at random from the culture from 

 ivhich were derived the conjugants employed in the experiment. The unit of measure 

 is 4 microns. 



41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66| 67 68 69 70 



No. of 

 specimens 



1 1 



5 4 6 



8 813 



91818 



11 



911 



12,11 



10 



the matter ('11) it was found that in Svild' cultures of Paramecium 

 caudatum, such as we are here dealing with, the coefficient of 

 correlation in size due to assortative mating averages about 0.380. 



In the culture from which our conjugants of the present Experi- 

 ment 16 were derived, there were measured 92 conjugating pairs 

 (184 specimens), and 180 non-conjugants. The results of these 

 measurements are given in tables 1 and 2. The unit of measure- 

 ment was 4 microns. 



The non-conjugants varied in length from 164 to 280 microns, 

 the mean length being 222.890 ± 1.020 microns, with a standard 

 deviation of 20.299 ± 0.722 microns and a coefficient of varia- 

 tion of 9.099 ±0.323 per cent. 



The conjugants showed, as always, less variation than the 

 non-conjugants; the length varied from 168 to 236 microns. 



