INFUSORY WORMS. 347 



become pretty generally known, than immediately, as if by a kind 

 of fatality, the animalcular doctrine was carried a great deal too far; 

 and innumerable substances were supposed to swarm with these 

 minute beings, which later and more accurate observations have 

 proved to be totally free from them. Thus, the blueish or bloomy 

 appearance on the surface of several sorts of plumbs, grapes, and 

 many other fruits, has been supposed owing to innumerable legions 

 of animalcules on the surface of the fruit : but this idea is entirely 

 erroneous. It happens, a little unfortunately, that Mr. Pope has 

 introduced it into his celebrated poem, the Essay on Man, which still 

 continues to propagate the mist ike amongst those who are not scien- 

 tifically conversant in such subjects. 



" Ev'n the blue down the purple plum surrounds, 

 " A living world, thy failing sight confounds." 



The blueish appearance above-mentioned is a mere vegetable 

 efflorescence, which regularly takes place on ^uch kind of fruit, and 

 consists of particles of no determined shape, and has not the least 

 appearance that could lead to a supposition of its being of an ani- 

 mal nature. 



To attempt a methodical enumeration of animalcules 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 parti- 

 cular times from what they did the moment before ; and others, 

 though their form is constant, are apt to vary in colour; by which 

 menus some deception or obscurity may arise, and an un< ertainty in 

 determining 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 pos- 

 sess 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, we 

 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 vorticella is one of the principal. 

 Its character is, that the mouth or opening is surrounded by nume- 



