252 A Biometrical Study of Conjugation in Paramecium 
of conjugating Pararaecia as they occur under normal cultural conditions. But 
although these results demonstrate the existence of a high correlation, they thereby 
immediately direct attention to tlie very interesting and important question as to 
what its origin and meaning may be. The purpose of the further analysis is to 
throw liglit, if possible, on these problems. 
The first point needing consideration is the character of the regression for 
these direct correlations. In order to show this, I have prepared diagrams giving 
the means of the arrays and the fitted regression lines, for the three direct correla- 
tions of Series A. Diagram VI. gives the regression of the length of B on the 
length of A ; Diagram VII. tlie regression of breadth of B on breadth of A ; and 
Diagram VIII. the regression of index of A on index of B. 
There can be no doubt of the essential linearity of the regressions. The 
diagrams show very clearly the regularity with which an increase in the size of 
one member of the conjugant pair is accompanied by a proportional increase in 
the other member. 
The cross correlations may now be examined. Neglecting the indices, which it 
hardly seems worth while to consider separately in the cross correlations we have 
for each group two possible cross con-elations, viz., length of A with breadth of B, 
and length of B with breadth of A. Cross correlations for the short series 
Series A. 
147.5 
182.5 
187.3 
192.5 
142.5 147.5 152.5 157.5 162.5 1675 172.5 177.5 182.5 187.5. 192.5 1975 
Length of A. 
Diagram VI. Eegression line for the homogamic correlation between the lengths of the individuals 
of conjugant pairs in Series A. (See footnote, p. 241.) 
