CLASSIFICATION. 51 



malcules abound, so that the student may not be 

 at a loss as to their nature when they are met with. 



Infusoria are comprised under two great classes, 

 Polygastrica and Rotatoria ; the former being dis- 

 tinguished by appearing to have numerous vessels, 

 or stomachs, for carrying on digestion, and the 

 latter having but one. This is Ehrenberg's 

 method of classifying them ; and though Meyen 

 and others think the vessels of the first class are 

 not stomachs, the name must be retained until 

 the fact is ascertained. 



After some experience in viewing animalcules 

 with a glass, their general form and outward 

 appearance is sufficient to enable the observer to 

 determine in which class to place them. The 

 Rotatoria have usually a foot near the extremity 



