Raymond Pearl 
249 
VI. Assortative Mating in Conjugation. 
We come now to the consideration of the problem which originally led to the 
taking up of this work. This problem was : Is there any definite tendency for 
individuals relativel}' alike in size to conjugate with one another ? It seemed to 
me at the outstart that though conscious choice, or any selection factor depending 
on a sexual differentiation, were obviously out of court, yet theoretically it was 
by no means impossible that a sensible degree of correlation between conjugants 
might exist. Thus the nature of the conjugation process itself made it seem 
possible if not probable that the two individuals in a conjugant pair must 
reasonably well "fit" one another if the conjugation were to be successful. Also 
it was not at all difficult to conceive that this sorting out of "fitted" pairs might 
be accomplished in a perfectly mechanical way when Jennings'* work on the 
reaction of the organism was considered. The difficulty of course came in con- 
ceiving that the " fit " of the two individuals would have to be any better, to 
ensure successful conjugation than we should in the long run get by pairing 
altogether at random individuals in the same culture. It seemed to me altogether 
likely that this condition was what actually existed, and I fully expected when 
the work was begun to find that putting together at random pairs of individuals 
would lead to just as high a coefficient of correlation between the members 
of the pairs as we should find from actual conjugants. How far from the facts 
this expectation was, the results which follow will show. The plan which was 
adopted to reach a solution of this question of assortative pairing was to deter- 
mine by actual measurement the degree of correlation between the same and 
different characters in conjugated pairs and then to determine by experimentally 
pairing at random the records for these same individuals what degree of corre- 
lation we have between the individuals of a pair when there is no assortative 
mating whatever. Also it seemed desirable to find out what would be the 
result of putting together at random pairs of non-conjugants and pairs in which 
one individual was a conjugant and the other a non- conjugant. 
A word should be said regarding the practical methods followed in this portion 
of the work. The first point which needs attention is one regarding the order of 
entry of individuals into the correlation tables. Suppose we call the individual of 
each conjugating pair which was the first to be measured A, and the individual of 
the pair last measured B. Then if, as was actually the case, there is no selection 
of the first individual to be measured on the basis of size characters, but instead the 
choice of A is quite accidental, then clearly the biometric constants for the A 
individuals ought not to differ significantly from those for the B individuals. As 
a matter of fact they did not differ significantly. Consequently it is a matter of 
indifference, so long as we are dealing with the same character in both members of 
the pair, whether .4 or £ is entered into the correlation table as the first variable. 
* Various papers in Amer. Jour. Physiol., Amer. Naturalist, Amer. Jour. Psychol., etc. Specially 
for the reactions preceding conjugation, cf. Jour. Comp. Neurol, and Psychol. Vol. xrv. pp. 441 — 510. 
