42 



Animalcules," was, for a long time, the only treatise on 

 the subject, to which the observer had access, and that, 

 however valuable, not affording sufficient means of identi- 

 fying all the objects that were found, with forms previously 

 known, much that was presented to view under the micros- 

 cope, passed unrecorded, and only occasionally, as some- 

 thing of uncommon interest appeared, it was committed to 

 paper. Subsequently, the acquisition of Ehrenberg's mag- 

 nificent work on the Infusoria, afforded the means of 

 comparing American forms with the figures given in that 

 work, and such as could be identified with those figures, 

 have been recorded; as for the rest, not having skill in the 

 art of drawing, and aware of the difficulty of conveying 

 accurate ideas of such objects by mere verbal descriptions, 

 they have been reluctantly omitted. 



In making the observations which have resulted in the 

 following list, much valuable assistance has been afforded 

 by Professor Bailey, not only in overcoming the difficulties 

 incident to microscopical observations, but also for a large 

 amount of interesting microscopic objects, the fruit of his 

 own untiring investigations, or received from his foreign 

 friends and correspondents, all of which he has most 

 liberally imparted, 



Ehrenberg divided the Infusoria into two classes, viz : 

 the Polygastrica, and the Rotatoria (wheel-bearers,) so 

 called from the action of cilia around the mouth, which 

 resembles in their economy, the rotation of the spokes of 

 a wheel. 



POLYGASTRICA 



Comprehends 22 Families, 123 Genera, 553 Species. 

 Fam. 1. Monadina Genera 9. Species 26. 



2. Cryptomonadina " 6. " 16. 



3. Volvocina " 10. " 18. 



4. Vibriona " 6. " 14. 

 6. Closterina «' 1. " 16. 



