Kaymond Pearl 
55 
the base of this notch spring two flagella (cf. Fig. 1, p. 56). Its nutrition is sapro- 
phytic and the usual method of reproduction is by longitudinal fission. An 
excellent account (Avitli figures) of this organism has been given by Biitschli (1878). 
Material and Methods. 
The material on which this study is based was taken from two cultures set in 
the ordinary way for rearing Protozoa with pond-water and decaying plant material. 
One of the cultures was made with dry hay and pond- water (Culture B), and the 
other (Culture A) with dead and decaying water-plants from the same source as 
the water itself The source of the water in both cultures was the same. Both of 
these cultures ran the ordinary course, rising to a maximum of animal and plant 
life and then gradually falling off. Both passed through a stage in which Ghilomonas 
was especially abundant. The associated organisms were in general the same in 
both cultures, the most abundant forms, in point of numbers, being Paramecium 
caudatimi and a large SimHllmn. In the hay culture Ghilomonas was extremely 
abundant and very evidently in a flourishing condition when the samples were 
taken for measurement. Judged by the standards of (a) abundance, (b) size of 
individuals, (c) appearance of the protoplasm, and (d) activity, it could only be 
concluded that the environmental conditions in Culture B at the time the samples 
were taken were at an optimum for Ghilomonas. The series taken from this 
culture, which will be designated throughout the paper as Series B, may, then, be 
considered to represent the prevailing condition (for this particular race, of course) 
of Ghilomonas growing ur^Aev favorable circumstances. 
On the other hand, when the samples were taken for measurement from 
Culture A the conditions were very different. This culture had at that time passed 
the optimum for infusorian life, and all the organisms were rapidly disappearing. 
All the Paramecia, which had previously been abundant in the culture, had dis- 
appeared, and the numbers of individuals of Ghilomonas and Spirillum were being 
rapidly reduced. Some notion of the rapidity with which this reduction was going 
on may be gathered from the fact that on the day following that on which the 
samples were taken one could only with difficulty find specimens of Ghilomonas, 
while on the second day after the sampling careful search failed to obtain any 
specimens. The culture had apparently completely "run out " as far as infusorian 
forms were concerned. The series taken from this culture (Series A) may be con- 
sidered to represent the character of the local race of Ghilomonas when living 
under the most unfavourable environmental conditions which the individuals were 
capable of withstanding in the active state. It will thus be seen that the 
individuals of Series A were in a sense practically the ultimate "survivors " of the 
progressively worsening conditions of the culture. But it must be understood that 
this does not mean that they were survivors in any process of destruction of the 
race. Ghilomonas, in common with most other infusoria, encysts when the environ- 
mental conditions become so unfavourable that it is unable to withstand them any 
longer in the active condition. The cysts of Ghilomonas have been figured by 
