INFUSORIA. 135 



others, the Vorticellce, there is but one stem with a sin- 

 gle bell-shaped body on the end, but the stem contracts 

 into close spirals and suddenly draws the animal down. 

 When the danger is past, the stem slowly uncoils, the 

 branches spread themselves, the animals expand, and all 

 is as before. Indeed, the variety of form and habit in : 

 the Infusoria is almost infinitely great. 



The general opinion is that "animalcules" have no 

 color. This is a mistake. The majority are almost col- 

 orless, but green, crimson, yellow, indigo blue or almost 

 black Infusoria are not uncommon, and the loricse, as" 

 stated, often become brown. 



The free-swimming Infusoria are more abundant than 

 the attached ones, and much more difficult to examine 

 because they will never stand still. But how do these 

 creatures, all of which are invisible without the micro- 

 scope how do they move ? For this purpose they have 

 organs of two kinds, and they are separated into two 

 great classes according as they possess the one kind, or 

 the other. In some there are one or more long, color- 

 less lashes which extend from the front of the body> 

 beat against the water, and so row the animal about very 

 rapidly. Each of these lashes is called zflagellum (ipln- 

 T2\, flagella). In others there are on the body short, 

 very fine hairs, which are continually vibrating so rap- 

 idly that they are often invisible even under a high- 

 power objective. The short hairs are called cilia, and it 

 is their action on the water that urges the animal about 

 even more quickly than the flagella. The cilia may be 



