1900-1.] Dr J. Y. Simpson on Binary Fission of Ciliata. 403 
organ is entirely formed anew, the position of the original one 
usually decides upon which of the daughters this work devolves. 
Be it in the anterior portion of the parent, it is generally found 
that the daughter that develops from the posterior half will have 
to form the new organ. Of Paramecium , however, it may be said 
that the mouth lies as a rule slightly in the posterior half of the body ; 
and in this particular instance the new mouth is always formed 
behind the old one, and this involves considerable consequent dis- 
placement. One or two abnormal Paramecia , in which the mouth 
lay unusually close to the tail, gave one the opportunity of verifying 
the correctness of this exception, even in such extreme cases. It 
is, however, the anterior contractile vacuole that is formed anew in 
either daughter. 
In the case of the Hypotricha there is a renewal of the whole 
ventral ciliary apparatus of both daughters as a consequence of 
division : the same phenomenon occurs after conjugation. The 
process has been studied by Stein, Balbiani, Engelmann, Sterki,* 
and Prowazek,f and even yet we cannot claim to know all the 
details. I have attempted to follow the process in the case of 
Stylonichia, the favourite object of examination, but it is a work 
of exceptional difficulty. Previous to division, new frontal cirri are 
formed in the anterior half of the dividing creature, practically 
under the old : they are remarkably transparent and clear. Then 
follow in succession, according to Prowazek, the new adperistomal 
cirri, and finally the still insignificant anal cirri. Behind the 
marginal cirri the rudiments of their successors are formed at the 
same time ; they have a very crowded appearance. “ The new 
adoral membranellse arise close behind the old, so that at a later 
stage the latter seems ruptured.” This sentence settles the one 
point most in dispute among the older workers as to whether the 
adoral zone was renewed or not. Personally I have no doubt of 
the fact. Much the same can be also observed in what will be the 
posterior daughter. The new cirri appear first as cilia, and are 
very irregular and often violent in their motions, contrasting with 
* ‘ ‘ Beitrage zur Morph ologie der Oxytrichinen,” Zeitschr. f. wiss. Zoologie , 
Bd. 31, p. 29 ff. 
t ProtozoenstucLien : Arbeiten aus den Zoolog. Instituten des Universitat. 
Wien , Tom. xi., Heft, ii., 1895-1899. 
