WHAT CONDITIONS INDUCE CONJUGATION IN 
PARAMECIUM? 
H. S. JENNINGS 
Henry Walters Professor of Zoology, Johns Hopkins University 
FOUR FIGURES 
Why are Paramecia found to conjugate at certain periods 
while at other periods they multiply without conjugation? AA'^ork 
undertaken on the relation of conjugation to heredity and vari- 
ation in these organisms has forced me to deal with this ancient 
problem. In the present paper I propose to give briefly, and with- 
out entering upon the history of the subject, an account of experi- 
ments and results upon this question. Discussion of the literature 
is reserved for a later and more extensive paper dealing with 
the effects of conjugation upon the organism and upon its life 
history . 
The conditions producing conjugation have been sought ia 
two different directions: on the one hand, in certain external 
conditions; on the ocher, in certain internal conditions. 
The commonest view is perhaps the following: The life of 
these animals proceeds in cycles. There is a long period of multi- 
pUcation without conjugation. Diiring this period there is a 
gradual decrease in vitality, showing itself in degenerative changes 
and in a decrease in the rate of multipUcation Finally the animals 
can divide no more, and will die if conjugationor some equivalent 
process does not occur. Now they are ripe for conj ugadon. Con- 
jugation is therefore due to a certain internal condition of 
maturity in the orgaaism. For a presentation of this theory, see 
Calkins' recent valuable work ''Protozoology" (1909). 
