134 AQUATIC MICROSCOPY FOR BEGINNERS". 



and delicate. Some of them are so flexible that 

 they can double and twist themselves almost as well 

 as a worm can writhe. Others are hard, and some 

 even are covered by a transparent case secreted from 

 their own body. This case is called a lorica, and is 

 used as a shelter for the soft and otherwise defence- 

 less animal. When frightened, such forms quickly, 

 withdraw themselves to the bottom of the lorica, and 

 remain there in a little, almost shapeless, heap, until 

 the danger is past. Then the enclosed Infusorium 

 will slowly rise to the front of the lorica, protrude the 

 front part of the body, open the organs by which it 

 creates currents in the water, and there fish for the 

 food those currents bring to its mouth. These loricse 

 are usually permanently attached to plants or to other 

 submerged objects. They are also generally trans- 

 parent and colorless, but sometimes, as they become 

 old, the color changes to a rich, translucent chestnut- 

 brown. 



In other Infusoria the loricse are not hard and .trans- 

 parent, but soft and opaque, yet delicate. These are 

 usually made of innumerable little particles of dirt 

 fastened together by a sticky substance secreted from 

 the ani'Tial's body. Almost any small particles float- 

 ing about and striking against the sticky mass will be 

 pretty sure to adhere, and so help build up the soft 

 sheath that serves the Infusorium as a protective cov- 

 ering, and sometimes effectually conceals it from 

 the microscopist who may be seeking it. 



But these soft and granular loricse are not formed 

 entirely by accident. They are built chiefly of those 

 little particles brought to the animal by the currents 

 produced by the organs it has for that purpose. These 



