PROTOZOAN FAUNA OF HAY INFUSIONS 261 
the surface of either of these infusions, and at the bottom it was 
only observed in BI. At the point marked x (fig. 12) fully 95 
per cent of the animals were conjugating. Nevertheless the par- 
amaecia fauna at the bottom ran practically the same course in 
each infusion, in fact it survived somewhat longer in the infusion 
in which conjugation was not observed. This culture also illus- 
trates a case in which a temporary decline in numbers occurred 
immediately after an epidemic of conjugation (ef. Mmgst2)p 
Fig. 15 BIV group. Vorticella fauna at the surface (----- ) and bot- 
tom ( Ne 
In group B III, in which there was an exceptionally large 
bottom fauna, conjugation was observed among the paramaecia 
at the surface and bottom simultaneously, but was somewhat more 
prevalent at the top. Fig. 13 shows that the epidemic occurred 
at the period of the surface maximum and that the ensuing decline 
at the top was coincident with a remarkably large increase in the 
bottom growth. 
Apparently many species of infusoria do not resort to conju- 
gation, to sustain rapid. cell division when the environment is 
slowly changing and the data give no reason for believing that 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, No. 2 
