VII. 



THE BELL-ANIMALCULE {Vorticelld). 



The bell-animalcule is one of a very large group of animals 

 called the Infusoria^ on account of the fact that many mem- 

 bers thereof make their appearance in infusions of certain 

 animal and vegetable substances. 



The higher multicellular animals begin their existence as 

 simple nucleated cells, and the single nucleated cell which 

 constitutes the whole animal in its primitive condition 

 divides and subdivides until an aggregation of similar cells 

 is formed. And it is by the differentiation and metamor- 

 phosis of these primitively similar histological elements that 

 the organs and tissues of the body are built up. In the 

 Infusoria, the protoplasmic mass which constitutes the germ 

 does not undergo this process of preliminary subdivision, 

 but such structure as the adult animal possesses is the 

 result of the direct metamorphosis of parts of its proto- 

 plasmic substance. Hence, morphologically, the bodies of 

 these animals are the equivalents of a single cell; while, 

 physiologically, "they may attain a considerable amount of 

 complexity. 



The Infusoria abound in fresh and salt waters, and many 

 make their appearance, as before stated, in organic in- 

 fusions, their germs either being contained in the substances 

 infused, or being wafted through the air. Their diffusion is 

 greatly facilitated by the fact that many of them retain their 



