1900-1.] Dr J. Y. Simpson on Binary Fission of Ciliata. 421 
pustulata, and Oxytricha pellionella. It is of course true that 
ever so many negative results do not contradict one positive 
result, but I must confess that I am extremely doubtful concerning 
this phase of Joukowsky ’s work, and am entirely in agreement 
with Maupas 5 view.* 
The Trench biologist also maintained that conjugations between 
near relatives were sooner or later sterile. As I have already 
shown, this is possibly true in the case of conjugation between 
members of the two species of Paramecium. But in the case of 
Paramecium yutrinum , Joukowsky observed effective conjugation 
between the descendants of one individual ; at the same time he 
admits that this probably has its limits. I also am inclined to 
believe that this peculiar process has its limits — but in the Maupasian 
sense ; for although I have observed conjugation in the case of P. 
caudatum between the descendants of an exconjugate, in the four or 
five instances in which I kept them they all died off within four to 
eight divisions. 
* Joukowsky fails to observe that in Leucoyhrys patula and Paramecium 
putrinum Maupas recognised possible exceptions to his puberty theory ( Le 
Raj. Tcaryog. chez les Cilids. p. 410), while he also admits that the period of 
immaturity may be greatly shortened under certain unknown conditions. Of 
these conditions I have been able to find out nothing. 
