414 Proceedings of Royal Society of Edinburgh. [sess. 
majority were treated daily in a constant manner, given the same 
definite amount of food (calculated from previous experiments), 
and provided with a certain amount of fresh water at definite 
intervals. With the others I experimented in the amount of 
food given, in the period of time that they were left without any 
change of water, in the amount of water on the slide, and so on. 
In no single instance did I obtain such clockwork regularity 
as Maupas’ tables show. The slides, whose history is given, were 
amongst those that were treated with regularity so far as I was 
able, and consequently they were all treated alike. Hence a day 
like June 25, when but one of the slides shows a complete 
Maupasian division, appears to me to represent the more natural 
state of affairs, and for no reason more than this. Maupas’ table 
of Stylonicliia pustulata admittedly deals with a form that 
multiplies more quickly than Paramecium caudatum — possibly 
about twice as an average over all temperatures. But at the 
close of the first three weeks his Stylonicliia has divided no fewer 
than thirty-nine times with a temperature that ranged from 
15° to 19° C. Now, no one has laid more stress upon the influence 
of temperature in raising the rate of division than Maupas, and yet 
I do not find from the table that his high rates of division bear 
any relation to the temperature. Quite the contrary is the case, 
for out of the four occasions within the first three weeks on which 
the Stylonichia divided three times in 24 hours, on two of 
them the temperature was actually a degree lower than the previous 
day, when it divided a less number of times. Accordingly, 
although I believe that ultimately continued binary fission involves 
a certain degeneration, and that Maupas’ theory of the matter is 
largely correct, still it is altogether false to imagine that under 
natural conditions a Stylonichia will rush through 316 divisions 
in 4J months : that is to say, the validity of Maupas’ method is 
open to question, and where this is so the results are always in 
jeopardy more or less. 
I may refer here to two peculiar cases of division that came 
under my notice. On 13th May 1900 two paramecian ex conju- 
gates were isolated on a slide and subjected to ordinary culture 
treatment. On the 14th they were as before; on the 15th there 
were three; they remained at this number on the 16th and 
