CLASSIFICATION. 67 



malcules on which they feed to enter their mouth as a 

 httle whirlpool or vortex, and hence the diminutive term, 

 rorticella. 



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 handfuU 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 Iiad been too 

 small to attract my attention so long as it remained motion- 

 less. Eixing 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 anythiTig I had ever observed before. It 

 was in the form of a little crystal slu-ub, 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 



