418 Proceedings of Royal Society of Edinburgh. [sess. 
aspects of binary fission, I never employed cover-glasses : any 
infusorian requiring high-power examination was easily isolated. 
Maupas also states that in his damp chamber there was very slight 
evaporation, and that “ when it was necessary ” he made com- 
pensation for the loss with rain water. If he added food daily, it 
is difficult to see how it was never necessary in addition to make 
up for evaporation. If the latter had to be done at all, it were 
surely better to change the water in greater or in less quantity 
with regularity, and so give less occasion to bacteria to generate. 
I cannot say that I found the latter method unsuccessful when I 
tried it. 
Joukowsky kept Pleurotricha lanceolata for a period of eight 
months, in the course of which 458 divisions occurred, and during 
that time he got neither conjugation — not even when he starved the 
creatures and set them in pure water — nor evidence of degeneration. 
In a certain degree there is correspondence here with Maupas’ 
experiments on Stylonichia mytilus, where senile degeneration 
(which, however, Joukowsky did not find) did not seem to 
stimulate this species to conjugation as it did in the case of 
Stylonichia pustulata. Joukowsky, nevertheless, observed a certain 
shrinkage in size, which he found depended on the quantity and 
quality of food. The following^ is his temperature table : — 
30° C. 23° C. 15° C. 
13 xii. 1894 : 6 p.m. 1 individual. 1 individual. 1 individual. 
14 xii. 1894 : 6 p.m. 16 individuals. 8 individuals. 2 individuals. 
The question of degeneration is probably the most important 
that he raises. As we have already seen, Maupas distinctly states 
that at the end of the period of eugamy, which covers a definite 
number of divisions of the creature, senile degeneration sets in, 
which ends in death if conjugation does not intervene : we have 
also seen the method in which this degeneration expresses itself. 
On this subject he had already been challenged by Biitschli, who 
maintained that the fission capacity of the Ciliata was specially great 
and much in evidence after conjugation, but that thereafter it 
gradually ebbed away. If by this Biitschli meant that immediately 
after conjugation the rate of fission is above the normal, I can 
only say that I have never observed anything of this nature in the 
several forms that have come under my observation. But if, as 
