INFUSORIA. 103 
The Paramecians are propagated by spontaneous division, as 
already described. They abound, as we have said, in semi-stagnant 
water, or in pure water which is occupied by aquatic plants, some- 
times in such prodigious quantities that they become troublesome. 
They may occur also in flower vases where the water is not frequently 
renewed. 
The species of this genus have an oblong compressed body, with 
an oblique longitudinal fold, directed towards the mouth, which is 
lateral. They are sufficiently large to be observed with a common 
lens, or eye-glass. Paramecium aurelia is common in ditches, or 
‘ponds, and moats, with aquatic plants. 
Humboldt’s assertion is fully verified in the case of the Infusorian 
under consideration, which is often found with its parasites (vide 
Fig 28). These are small creatures, cylindrical in form, and previded 
with suckers. Swimming vigorously in the water, they devote them- 
selves to chasing the Paramecium. When they have overtaken the 
fugitive, they throw themselves upon it, and establish themselves 
there. They soon multiply in the interior of its body, and their 
progeny suck and devour the unfortunate animalcule, which thus 
serves them at once for dwelling-house and larder. 
Another of the parasites which prey upon the Paramecium, in 
place of pursuing it, remains perfectly quiet until one of these 
approach, when it throws itself upon its victim, and is carried along 
with it. It buries itself in the body of the Paramecium, and, in a 
short time, multiplies to such a degree, that sometimes fifty of them 
are found on a single individual. 
The species of the genus /Vassu/a have the bedy entirely covered 
with cilia ; they are ovoid or oblong in form, contractile, their mouth 
is placed laterally, and provided with a circlet of teeth in the form of 
a wheel (zassa), this circlet dilating and contracting according to the 
size of the prey which it would swallow. They will either advance to 
seize the prey, which the movement of the vibratile cilia have failed 
to draw within the vortex of their mouth, or, as in the case of the 
Paramecium, they are sometimes obliged to seek for their prey. 
These curious Infusoria live in fresh water, feeding on the débris of 
aquatic plants, from which they draw their chief nourishment. Their 
colour is white or greenish, sometimes a brownish green, variegated 
with violet vesicles. 
The genus Bursaria contains animals with an oval or oblong con- 
tractile body, provided also with vibratile cilia on the surface, having 
also a large mouth, surrounded with cilia, forming a sort of micro- 
scopic moustache, spirally arranged. 
