THE LIFE OF THE SIMPLEST ANIMALS 13 
The body is pear-shaped or bell-shaped, with a mouth 
opening at the broad end, and a delicate stem at the 
narrow end. This stem is either hard and stiff, or is 
flexible and capable of being suddenly contracted in a 
close spiral. In the body mass there is one pulsating 
vacuole and one nucleus. Usually many Vorticelle are 
found together on a common stalk, thus forming a proto- 
zoan colony. 
The life processes of Vorticella are of the simple kind 
already observed in Ameba and Paramecium. Vorticella 
shows, however, some modifications of the process of repro- 
duction which are interesting. The plane of division of 
Vorticella is parallel to the long axis of the pear-shaped 
body, so that when fission is complete there are two Vorti- 
celle on a single stalk. One of the two becomes detached, 
and by means of a circle of fine hairs or cilia which appear 
around its basal end leads a free swimming life for a short 
time. Finally it settles down and develops a stalk. Vorti- 
cella shows two kinds of fission—one the usual division 
into equal parts, and another division into unequal parts. 
In this latter kind, called reproduction or multiplication 
by budding, a small part of the parent body separates, 
develops a basal circle of cilia, and swims away. The pro- 
cess of conjugation also takes place among the Vortt- 
cella, but they are never two equal forms which conju- 
gate, but always one of the ordinary stalked forms and 
one of the small free-swimming forms produced by 
budding. 
Here, then, in the life of Vorticella, are new modifica- 
tions of the life processes ; but, after all, these-life processes 
are very simply performed, and the body is like the body of 
the Ameba, a single cell. Vorticella is plainly one of “ the 
simplest animals.” 
%. Gregarina.—A fourth kind of protozoan to which we 
can profitably give some special attention is Gregarina 
(Fig. 9), the various species of which live in the alimentary 
