INFUSORIA. 



n 



thickly as they can lie, into patches. They constitute the 

 genus Vibrio. Several may be seen among them briskly 

 -wriggling along, which resemble a little coil of spiral wire. 

 Such forms bear the generic appellation of Spirillum.* 



As all infusions of vegetable or animal substances are 

 found to be speedily filled with animals resembling these, 

 in great variety, though not always of the same species, 

 the circumstance has been seized by naturalists to afford 

 a name by which this class of beings should be distin- 

 guished. They have been therefore called Infusoria, or 

 infusory animalcules ; a very extensive group, and one 

 which, in a more advanced state of our knowledge, it may 

 be found desirable to divide, since it includes animals of 

 very different grades of organisation. Those of -which we 

 have spoken are among the simplest of these forms : we 

 shall now describe others of a higher place in the scale, 

 and more attractive in their appearance and in their 

 habits. Every day during which the infusion is allowed 

 to stand, it will display fresh forms, and generally those 

 which appeared most abundantly in the earlier stages will 

 be found successively to die out, and be replaced by other 

 species. The more highly organised kinds will usually 

 be discovered at the later periods. 



But there is a very beautiful form, and one which can- 

 not fail to possess great interest for the young microscopi- 

 cal student, which commonly occurs pretty early. Perhaps 

 we shall see some of the stalks of the macerated hay, or 

 floating portions of the semi-decomposed leaves, clothed 

 with what appears to the naked eye to be a veiy delicate 



* Recent researches, however, render it probable that these are the earliest 

 stages of Intestinal Worms. 



