222 MICROSCOPY FOR BEGINNERS. 



short, free - swimming life. "When once attached they 

 are adherent till death. The animals themselves are 

 small, but often apparent to a trained eye ; they are al- 

 ways visible under a good pocket-lens. The colonies, how- 

 ever, of all the fresh-water forms need no magnifying; 

 some of them are very conspicuous. These communi- 

 ties are formed of the protective coverings or sheaths 

 secreted by the animals. Some take the form of very 

 narrow, brownish tubes, adherent to the lower surface 

 of floating chips, boards, waterlogged sticks, or even 

 occasionally to lily -leaves or the submerged stems of 

 grasses. The little tubes branch like miniature trees, 

 and spread over the surface as if the delicate tree had 

 been flattened down and pressed so hard that it could 

 never again rise up ; or they may be attached by the 

 base only, the trunk and the branches then floating 

 and waving in the water. The animals secreting these 

 tubes live in them, projecting a part of the body beyond 

 the orifice, and very quickly retreating when frightened. 

 And they are usually very timid, retiring into the tubu- 

 lar home at a slight disturbance of the water, needing a 

 long time in which to recover and again look out at 

 the entrance and spread their beautiful tentacles. 



In other forms the colony is surrounded by a thick, 

 rather firm, jelly-like material, from which the animals 

 protrude themselves, and into which they retreat. These 

 jelly masses are usually colorless and semitransparent, 

 or they may be tinged a pale red. They are to be found 

 in the purest of still water, adherent to sticks, capping a 



