LECTURE XII. 2H 



malcules appears, at first view, almost a hopeless 

 labour; since exclusive of the vast variety of 

 species, (of which, in all probability, only a small 

 part has yet been observed,) many of them have 

 a power of changing their shape at pleasure ; so 

 as to appear widely different at particular times 

 from what they did the moment before; and others, 

 though their form is constant, are apt to vary in 

 colour; by which means some deception or ob- 

 scurity may arise, and an uncertainty in determin- 

 ing the species. Much, however, has been done: 

 a great many species of Animalcules have been 

 perfectly well described, and are perfectly well 

 known to microscopical observers, since they 

 possess characters too clear and plain to admit of 

 any doubt of their species, whenever they happen 

 to appear. 



As examples of this curious and interesting 

 race of animals I shall particularize a few of the 

 most remarkable kinds, and such as are well figured 

 in the works of Naturalists. 



Among these the genus called Vorticetta is one 

 of the principal. Its character is, that the mouth 

 or opening is surrounded by numerous short 

 feelers, forming a kind of fringe round the head. 



