THE CILIATE INFUSORIA. 39 
away, both assuming the common form of the animalcule 
when free-swimming, and differing from the original indi- 
vidual only in being of smaller size.” 
The most complicated as well as most interesting form of 
all the Infusoria is the bell-animalcule, Vorticella. It is 
very common in pools, forming patches like white mould on 
the leaves and stems of submerged plants. It may, like 
Stentor, be observed under low powers of the microscope. 
Their motions, as they suddenly contract and then shoot 
out their bell, mounted ona long stalk, are very interesting. 
The throat (cesophagus) is quite distinct, while the nucleus 
is the most conspicuous organ of the body. The digestive 
cavity is a large hollow in the protoplasm forming the body- 
mass, in which the whole mass of food revolves in a deter- 
minate channel. Closely allied to Vorticella is Hpistylis 
(Figs. 27 and 28). 
While most ciliate Infusoria, so far as known, multiply 
by self-division, i in Vaginicola the process is more like true 
gemmation or budding, and is accompanied by a process of 
encysting, resulting in the production of a free-swimming 
ciliated embryo, the adult Vaginicola being attached. The 
Vorticella also becomes encysted, and the nucleus subdivides. 
until the body, becomes filled with monad-like germs, the 
result of the simultaneous breaking up of the nucleus. The 
Vorticelle, then, pass through a flagellate or monad stage, 
from which they pass into the Vorticella condition, when 
they multiply by self-division and by budding, the last 
generation becoming encysted. 
Conjugation is a common occurrence in ciliate Infusoria, 
and results in the breaking up of the nucleus of each indi- 
vidual into a number of fragments, and the appearance in 
each of the individuals of the nucleus and nucleolus (either 
single or multiple) which characterize the species. * 
* Baitbiani believes that the ciliate Infusoria have eggs which are 
fertilized by spermatic particles. Morerecently, however, Engelmann, 
Biitschli, and Hertwig have denied that conjugation is of a truly sexual 
character, and that the striated nucleoli of certain individual Infusoria 
are spermatozoa. ‘‘ Nevertheless,’’ remarks Huxley (Anatomy of In- 
