420 Proceedings of Royal Society of Edinburgh, [sess. 
appendages. Still, none the less am I convinced of a gradual 
ebbing of vital energy as the series proceeds, which expresses 
itself in slowed motion, in a tendency to inactivity and general 
listlessness (if the word be admissible in this connection), as also 
in a certain diminution in size that was not remedied by any 
amount of food. 
Joukowsky also made observations on a culture of Paramecium 
caudatum. In a temperature of 19°-23° C. he got them to divide 
one or two times. By the seventh month he noticed that they 
divided badly. Some of the individuals seemed dead, but on 
examination they were found to be still alive. The cilia on the 
upper surface had almost completely disappeared ; indeed it was 
only at either end and in the region round about the mouth that 
he found ciliation at all. He made out, however, no hint of nuclear 
degeneration. 
Maupas laid great stress on the period of immaturity in the 
infusorian’s life — that definite number of divisions previous to 
puberty that had to be gone through before it was in a fit state to 
conjugate. We saw, e.g., that this period was reached by 
Stylonichia pustidata at the 130th division. Joukowsky, experi- 
menting with Paramecium jputrinum , found that this period of 
puberty was attained after some seven or eight divisions, that is to 
say, it is practically always present. In this particular species he 
succeeded in getting exconjugates to conjugate within that small 
number of divisions, and maintains in consequence that Maupas’ rule 
does not have universal validity. How it is well known that by 
means of starvation not only can Ciliata be prevented from multiply- 
ing by binary fission, but after they have reached the period of puberty 
they can be hurried into conjugation by a similar method.* I 
therefore made deliberate attempts, by means of starvation and 
other unfavourable means, in another series similar to that of which 
details have already been given, to induce conjugation within the 
period of puberty, but never succeeded. The forms experimented 
with were the two Paramecia ( aurelia and caudatum ), Stylonichia 
* With regard to the former point, we may note that those Ciliata that 
have been hindered in this way from reproducing themselves by binary 
fission require some little time to recover the power to do so when food is 
again supplied to them. 
