CLASSIFICATION. 67 
malcules on which they feed to enter their mouth as a 
httle whirlpool or vortex, and hence the diminutive term, 
Vorticella. 
The first that I ever observed was one of the most beau- 
tiful and most conspicuous of them—the arborescent Vorti- 
cella. I had brought from a pond a handfull of aquatic 
plants, and having put them into a vase with fresh-water, I 
soon found, as I expected, that I had made several green 
Hydras prisoners. While I was watching their movements, 
I observed a sudden jerk in something that had been too 
small to attract my attention so long as it remained motion- 
less. Fixing my eye on it, it increased in size, and having 
remained motionless for a little, by another sudden jerk it 
became so small that it was almost invisible. Having 
watched these changes for some time, I saw that it had life, 
and bringing it near to the side of the glass, and employing 
a pretty powerful lens, I saw that what to the naked eye 
had seemed a little transparent haze, was a beautiful little 
creature, unlike anything I had ever observed before. It 
was in the form of a little crystal shrub, the branches of 
which were dichotomously divided, every branch terminating 
in what resembled a little bell-shaped flower. Further ob- 
servations led me to know that the sudden changes of size 
