PARAMAECIUM AURELIA AND PARAMAECIUM CAUDATUM 233 
material left over after the daily isolations from my pure lines, 
I have failed to observe a single syzygy, either between aurelia 
lines or caudatum lines, or between aurelia and caudatum lines. 
Jenning’s” experiments on conjugation in Paramaecium bring 
out data which add further evidence that in certain strains at 
least a predisposition to conjugation does not exist. Maupas 
wrote: ‘“C’est bien certainement une des espéces (aurelia) qui 
se recontrent les plus fréquemment 4 l’etat conjugué.”’ 
Maupas, as we have seen, pointed out a difference in the nuclear 
phenomena during conjugation which he held to be of diagnostic 
value, and Hertwig apparently showed that aurelia has two micro- 
nuclei at the reorganization after conjugation. Calkins, on the 
other hand, has shown that P. caudatum, in one case, reorgan- 
ized with two micronuclei and later reverted to the uninucleate 
type. Such a case can readily be considered a ‘sport’ which has 
arisen possibly by the persistence of the stage with two micro- 
nuclei immediately following the separation of the conjugants, 
or by the precocious division ef a single micronucleus previous to 
the first regular vegetative division after conjugation. Although, 
as Calkins stated also, forty-five generations is a long time for 
an abnormality, if it be such, to persist; nevertheless, I believe 
it is very significant that, whereas during the presence of two 
micronuclei the division rate averaged only 0.8 of a division per 
day, after the loss of one of the micronuclei the division rate 
increased to the remarkable rate of 2.2 divisions per day, on the 
average for a period of four months. It is also of interest that 
the other exconjugant which reorganized ‘normally’ as caudatum 
failed to live. 
So far as I am aware, the following statement?’ by Simpson is 
the only record of a possible case of conjugation between aurelia 
and caudatum: ‘‘Out of twenty-one attempts I had but two par- 
tial successes. Conjugation took place on two slides: the period | 
was normal. After separation each of the ex-conjugates divided 
once: on the third day they died off. In anticipation of something 
22What induces conjugation in Paramecium? Jour. Exp. Zodl. 9, 2, 1910. 
Observations on binary fission in the life-history of Ciliata, Proc. Royal 
Soc. Edinburgh, 1901, pp. 407-408. 
