CONJUGATipN IN PARAMECIUM 
295 
Whether, when conjugation does occur, the external conditions 
favoring it are the same for the other races as for k is a question 
of interest, but also of difficulty. In most cases where other races 
were seen to conjugate, the conditions were similar to those des- 
scribed above as favorable for the strain k. Usually there is a 
period of rapid multiplication, owing to abundant nutrition; this 
is checked, and an epidemic of conjugation results. With this 
the experience of other writers seems not inconsistent. 
The fact that diverse races of Paramecium differ so greatly 
in respect to conjugation is evidently deserving of careful consider- 
ation in all experimental work on the life history of these organ- 
isms, and on the physiology of conjugation. Certain strains will 
be much more favorable for a given line of work than others, 
while investigators working with diverse strains are certain to 
reach discordant results. 
Woodruff ('08, p. 526) makes the following remark: ^'I 
oelieve it is customary to regard conjugation as of far more fre- 
quent occurrence than it actually is in the life history of ^wild' 
individuals, because it is brought to the attention in laboratory 
cultures and 'hay infusions' which pass through a series of changes 
— changes which inevitably bring about conditions unfavorable 
to the continued reproduction of the organisms, and which are 
compensated for by conjugation." In this connection it may be of 
interest to note that I have repeatedly found conjugation occur- 
ring under wild" conditions. This occurred in pools containing 
much decaying matter, where the water had largely evaporated. 
In such cases I found at times most of the individuals in conju- 
gation. Examination showed that conjugation was in progress 
at the time animals were collected. Furthermore, conjugation 
occurs very commonly under the following conditions: A quan- 
tity of water, containing Paramecia with much vegetation, is 
brought in from a more or less stagnant pool Nothing is added 
to this material, but the \egetation is allowed to begin decay in 
laboratory vessels. Almost invariably the Paramecia, if abun- 
dant, are found to begin conjugation inside of a week. There is 
of course no reason why the same thing should not occur in nature, 
when the same conditions are presented. The same conditions 
