ROTIFERS 221 
To us, the Hydras of the pond are insignificant, 
but if we can put ourselves in the place of Water 
Fleas, and small fry of that kind, we can faintly 
imagine that the Hydras are monsters from their 
point of view—monsters no less terrible than that 
described in the Greek story. In the classification 
of animals, Hydras are placed in the 
sub-kingdom Celenterata ; they are 
thus related to the Corals, Sea Anem- 
ones, and Jellyfish. 
I want you to look at the animal I 
have just taken out of this tube and 
placed under the microscope. It is 
the common Rotifer (Rotifer vulgaris), 
or, a8 some call it, the ‘‘ Wheel- 
animalcule.” It gets its name (Rotifer 
= wheel-bearer) from the two discs 
above the mouth, which seem to be 
rapidly going round like wheels. This 
circular motion of the discs is not 
Fie. 57.—THE 
actual, only apparent. The expanded «Winer 
discs are surrounded with very fine Awa at a. 
hairs, or cilia, which are in continual CULE,” OR 
motion when the animal is feeding. COMMON 
Their motion makes a little vortex, ROTIFER 
(ROTIFER 
or whirlpool, in the water, and by VULGARIS) 
this minute creatures in the water 
are sucked in and impelled into the mouth below, 
This species of Rotifer is a common inhabitant of 
ponds. Notice its cylindrical form, and the mouth 
and internal organs, which can be easily seen through 
the transparent body. When feeding, or at rest, 
the Rotifer attaches itself by a sucker-like foot to 
