238 AQUATIC MICROSCOPY FOR BEGINNERS. 



mals lead a short, free-swimming life. When once at- 

 tached they are adherent till death. 



The animals themselves are small, but often appar- 

 ent to a trained eye; they are always visible under a 

 good pocket-lens. Th* colonies, however, of all the 

 fresh-water forms need no magnifying; some of them 

 are even conspicuous. These communities are formed 

 of the protective coverings or sheaths.secreted by the 

 animals. Some take the form of rrarrow, brownish 

 tubes, adherenJ; to the lower surface of floating chips, 

 boards, waterlogged sticks, or even occasionally of 

 lily-leaves or to the submerged stems of grasses. 



The little tubes branch like miniature trees, and 

 spread over the surface to which they adhere 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 quickly retreating 

 when frightened. And they are usually exceedingly 

 ■ timid, retiring into the tubular home at a slight dis-r 

 turbance of the water, needing a long time in which 

 to recover and again to look out at the entrance, there 

 to spread their beautiful tentacles. 



In other forms the colony is surrounded by a thick, 

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

 mals protrude themselves, and into which they retreat. 

 These jelly masses are usually colorless and semi-trans- 

 parent, or they may be tinged a pale red. They are 

 to be found in the purest of still water, adherent to 

 sticks, capping a submerged stump with a cushion of 

 living jelly, clinging like crystalline globules to any 



