586 
THE YORTICELLA. 
Two species of Infusoria, termed Vorticella citrina and Stentor polymorphism may be found 
in soft water that has been allowed to remain in the open air, and in which any vegetable 
matter has been permitted to decay. Both 
these creatures are affixed by footstalks to 
some object on which they make their resi- 
dence, and both agree in having a bell-like 
mouth, edged with a fringe of cilia. 
These organs are set upon the edge of the 
mouth, and their object is indirectly to draw 
food into the system by creating certain cur- 
rents in the surrounding water. When the 
cilia are exposed to a good microscope, they 
appear to be formed like the cogs of a little 
wheel, which is rotating with great rapidity ; 
and it is not until a close examination de- 
tects the real cause of this appearance that its 
illusory nature is discovered. As in the case 
of the cilia attached to the higher animals, of 
which a notice has already been given, each 
fibril bends in regular succession, so as to pro- 
duce the effect of waves upon the eye. 
When the Infusoria are free, the continual 
movement of the cilia causes them to move 
with greater or lesser swiftness through the 
water, each fibril acting as a minute paddle, 
and having a distinct feathering movement, 
like that of an oar handled by a skilful rower. 
It is a most curious sight to observe the ad- 
mirable manner in which they make their 
strokes, the flattened sides striking the water 
so as to give the greatest force to the blow, 
and the back stroke being made with the edge, 
so as to meet with the least possible resistance. 
In the Yorticella, the footstalks on 
which the bell-like cup is seated are of consid- 
erable length, and capable of being shortened 
by being coiled into a spiral form. This is by 
no means an uncommon Infusorian, and is very 
liberal in displaying this capability. It is 
usually found associating in groups, so that 
there is hardly a stage in its life of which 
some example cannot be discovered. Though 
devoid of apparent organs of sense, this crea- 
ture is marvellously timid, shrinking in a 
moment if the water be shaken, and tighten- 
ing its coils until they resemble the spiral 
rings of a vine’s tendril. It soon, however, 
recovers itself, and by slow degrees permits 
STENTOR. Stentor polymorphis. (Two hundred times enlarged). the SpireS to Uncoil, and Waves its fringed 
head boldly in the narrow prison to which it 
has been consigned. Sometimes the Yorticella breaks away from its footstalks, and is then 
carried rapidly through the water by the action of its ever- waving fringe of cilia. 
As is the case with many of its kindred, the Yorticella is able to increase its numbers by 
the simple process of splitting itself into two distinct beings, each of which is afterwards a 
