260 BALANTIDIUM COLI. 



The Vacuoles are usually two. One lies at the posterior extremity 

 of the body, the other, separated from it by a varying distance, 

 is further forward on the ventral surface. Sometimes a third is 

 seen, and there are also cases in which only one is present- 

 usually the posterior, which is generally the larger. Their state of 

 tension varies exceedingly, and they become sometimes so full that 

 the surrounding substance is protruded like a hump, or the whole 

 body is deformed. The contractions are exceedingly slow and weak, 

 so that they easily escape observation. One sometimes sees the 



Fig. lii.^-Balantidium ooli in conjugation (after Wising). 



vacuoles perceptibly changing their position, and wandering from one 

 place to another. Stein observed them connected by a lacuna, and 

 the contents of the anterior one being conveyed to the posterior. An 

 opening to the exterior has not been observed. 



The Reproduction of Balantidium coli exhibits, according to Wising, 

 a process of conjugation (Fig. 129), in which the peristomial regions 

 are closely fused with one another, while the bodies remain quite 

 separate. The conjugating individuals present exactly the same 

 appearance as Stein described in Balantidium entozoon, except that 

 the changes of the nucleus and nucleolus, which occur normally in 

 the latter, have not been observed by Wising. Indeed, only a few 

 instances of conjugation have been observed, but quite enough to 

 convert the d^nori probable occurrence of the process into a certainty. 



Division is much easier to observe than conjugation. It is trans- 

 verse division which takes place here, as in the allied species, and 

 indeed in the majority of the Infusoria. Stein, Ekeckrantz, and 

 Wising have often observed it, and 1 have frequently noted it in my 

 later investigations. As regards some points of detail, I am forced to 

 differ somewhat from my predecessors. They describe the body of 

 Balantidium as simply constricting itself in the middle, after previ- 

 ous growth in length, yiSE?^^i,%(^'?99!?/^e nucleus, separating into 



