122 
Scientific Proceedings (44). 
since it is clear from many investigations that the reactions of 
paramcecia to various stimuli are greatly modified by the past 
and present environment of the organisms. 
74 (599) 
Conjugation of closely related individuals of Stylonychia. 
By GEORGE ALFEED BAITSELL. 
[Sheffield Biological Laboratory of Yale University.] 
A "wild" Stylonychia pustulata was isolated from a laboratory 
aquarium on October 1, 19 10, and placed on a "constant" beef 
extract medium. This culture, which consisted of four lines, was 
kept on depression slides and the animals were isolated daily. 
The medium proved to be a favorable one for this animal and in 
a period of about four months the culture reached the 350th 
generation. At that time (February 5, 191 1), when for ten days 
they had been dividing at an average rate of over three divisions 
per day (which was the highest rate of division that they 
had attained) a considerable number of conjugations between 
closely related cells occurred in the "stock" of the culture left 
over from the daily isolations. For a period of about three weeks 
this phenomenon was quite general in the stock and apparently 
would occur whenever a sufficient number of animals were present 
on a slide. To study the effects of conjugation, 132 conjugating 
pairs were isolated. These were kept in exactly the same kind of 
medium as that in which the conjugation had occurred so that 
the character of their environment was not changed by the isolation. 
From over 90 per cent, of the isolated conjugating pairs, ex-con- 
jugants were obtained (after a union of the usual duration) which 
were perfectly normal in general appearance and behavior. How- 
ever, none of these ex-con jugants divided and none lived 48 hours 
after separating. Animals obtained from "split" conjugating 
pairs also died without dividing. It was impossible to prolong 
the life of the ex-con jugants by any of the methods tried. Also 
from the time that the epidemic of conjugation made its 
appearance there was a continuous and rapid fall in the division 
rate of the main lines of the culture when averaged for ten-day 
