CONJUGATION IN PARAMECIUM 
283 
A large number of experiments were planned for the purpose 
of inducing conjugation between members of different races. 
Individuals of two races of very different size were placed to- 
gether in the same cultures, and subjected to conditions such as 
might be expected to briag about conjugation. Owing to the 
differences in size it was easy to distinguish the different races 
while thus living together. In these mixtures the race k was usu- 
ally one of the two constituents, since this race could always be 
depended on to conjugate. The race k was rather small in size — 
much smaller than L2 or D, but much larger than i; so that one of 
these three races was usually mixed with k. 
Almost invariably in such mixtures the individuals of k alone 
conjugated, those of the other race taking no part in the mating. 
This shows clearly that different conditions are required to induce 
conjugation in the different races. Some of the facts are as fol- 
lows : 
L2 and k were mixed October 8, 1908, with fresh hay. On 
November 6, k was conjugating, L2 was not. 
To this same mixture fresh hay was added February 18, 1909. 
On February 24, k was again conjugating, while L2 was not. 
The races k and i were mixed October 10, 1908; k conjugating 
October 19, i not conjugating. 
Fresh ha}' added to this mixture February 18, 1909; k conju- 
gating February 24, i not. Fresh hay added again February/ 24. 
New conjugation of k, March 1-3; i not conjugating. Another 
epidemic of conjugation in k, March 10. 
Three new mixtures of k and i made March 1, 1909. On March 
2 and 3, one contains conjugating k only; another pairs of both 
k and i. March 10, one of these mixtures has conjugating k, 
none of i. 
On February 24, 1909, a mixture was made of i and kh (this con- 
sisting of the progeny of a single ex-conjugant of k, isolated Novem- 
ber 9, 1908) . Fresh hay was added at the same time. From March 
2 to 8, kh was conjugating, while i was not. Again on March 26, 
kh conjugated in this mixture while i did not not. 
Thus out of eleven epidemics of conjugation in mixtures of 
which k formed a part, the conjugation was confined to k in all 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 2, 
