236 LORANDE LOSS WOODRUFF 
It is not only the presence of two micronuclei, but their pecul- 
iar morphology, as emphasized by Maupas, which is character- 
istic of the aurelia type. I have found one individual of the au- 
relia culture with three micronuclei, and a few specimens in 
which I have been unable, in total mounts, to distinguish a single 
micronucleus or more than one micronucleus. ~.But when only 
one micronucleus could be seen it has been of the aurelia type, and 
otherindividuals of the culture at the same period have had the two 
characteristic micronuclei. I have observed a variation in the 
number of micronuclei in various pedigree cultures of hypotrichs,*° 
Popoff has found reduplication in Stylonychia mytilus and Para- 
maecium caudatum during degeneration, and Kasanzeff has 
observed the same in starved P. caudatum. Thus, while my 
cultures of Paramaecium and various hypotrichous species sub- 
stantiate Wallengren’s and Calkins’ statement that the micro- 
nuclei are the most stable elements in the cell, and the last to be 
visibly affected by environmental changes, nevertheless it is 
apparent that they are subject to variations under certain 
unknown conditions. Temporary variation, therefore, cannot 
be considered as having weight in determining species. The essen- 
tial fact is, however, that throughout the existence of my aurelia 
and caudatum cultures, the morphology of the micronuclei has 
conformed to Maupas’ description for the respective species. 
It must be borne in mind also that P. caudatum has been the 
subject of more extended study by exact culture methods than 
any protozoon except P. aurelia, and in all these long pedigree 
cultures it has bred true to the caudatum type, at least with respect 
to the single micronucleus. Calkins, for example, in his impor- 
tant investigations on the life history of this form, carried three 
distinct cultures, by the aid of artificial stimuli during periods 
of physiological depression, through 379, 570, and 742 generations 
respectively. McClendon, also, studied mass cultures of Para- 
maecium for considerable periods and stated that he never 
found individuals ‘‘ with different numbers of micronuclei in the 
same culture.’’?! 
30An experimental study on the life history of hypotrichous Infusoria, Jour. 
Exp. Zodél., 2, 4, 1905. 
31Protozoan studies, Jour. Exp. Zool., 6, 2, 1909. 
