CONJUGATION IN PARAMECIUM 
285 
1909, and the animals began to conjugate three days later, Feb- 
ruary 27 (continuing till March 6). At the same time a mixture 
of kh with i was made; in this the specimens of kb were conjugating 
March 2 to March 6. There was no conjugation March 7, 8 and 
9, but on March 10, kh wsls conjugating freely again in both the 
pure culture and the mixture with i. Twenty-five pairs of progeny 
of kh were placed together March 10, and their progeny were con- 
jugating anew about two wrecks later (March 26) and again on 
May 11. There was likewise a new epidemic of conjugation in 
the original culture of kh on March 26. Not to enter into farther 
details, I may say that epidemics of conjugation were seen in 
the progeny of the single individual kh on the following dates: 
(1909) February 27 to March 6, March 10-13, March 26, April 
19, May 11, May 19, May 24, June 13, June 19, October 10, 
(1910) , January 29, February 24. (The long intervals between 
June and October and between October and January are due 
simply to lack of observations in those periods.) 
It is thus clear that the race k has a remarkable tendency to 
conjugate readily, even though the progeny of only one individual 
are involved. 
It was long held that the progeny of a single individual could 
not conjugate together without resulting in destruction. Calkins 
(1902, p. 175), however, observed conjugation in the progeny of 
a single individual without disastrous results, and the same thing 
had been observed for Paramecium putrinum by Biitschli (1876) 
and Joukowsky (1898). The general tendency of accurate work 
on the Protozoa has been to show that the importance attached to 
conjugation with animals of different descent was a mistake. In 
the conjugation of the race kh, above described, we have repeated 
conjugations within the progeny of a single individual, and the 
race is still flourishing. All of my races are indeed progeny of 
a single individual, and all save one have been seen to undergo 
repeated epidemics of conjugation, — in every case of course the 
progeny of a single individual conjugating together. The races 
are still flourishing, without indications of degeneration. I pro- 
pose to discuss the physiological effects of conjugation in a separate 
paper. Here, however, it is perhaps of interest to ask the further 
