FEESH-WATEE POLYP 81 



done by keeping the jars exposed to diffused light in 

 a warm room, and supplied with water plants and small 

 fresh-water crustaceans, as Daphnia, Cypris, etc. It 

 may be well to keep the jars covered to prevent evapo- 

 ration and the access of dust. From time to time the 

 jars may be set in the sunlight, in which case it is best 

 to darken the lower one-third of each jar by wrapping 

 it in a dark cloth or setting it in a close-fitting paste- 

 board ring made from a hat -box. In this way over 

 three hundred hydras were once raised during one win- 

 ter in a jar which in the previous autumn was known 

 to contain only about twenty specimens. Bits of raw 

 meat, hand-lens, dissecting needles, bristle, wire, tum- 

 bler, dilute acetic acid, and compound microscope will 

 also be required. 



Method of Examination. — Specimens are very likely 

 to be found on the lighted side of jars which have stood 

 near a window for some hours. Without disturbing the 

 jars in the least first examine the animals without and 

 with a hand -lens, noting as many as possible of the 

 characters given on the following pages; then, if the 

 hydra is attached to the side of the jar, by means of a 

 pipette suck the animal loose from its point of attach- 

 ment, previously loosening its attachment with a cam- 

 el's-hair brush, or, if fastened to a root of water plant, 

 snip off the root with a pair of fine scissors, transfer 

 with enough water to cover well to a watch-glass or a 

 concave slide in which the specimen may again be ex- 

 amined with the lens. If light-colored, the animal may 

 be made more plainly visible by placing the watch- 

 glass on a dark background, as a black book or dark 

 paper, or, if dark-colored, vice versa. Later, place the 

 watch-glass upon the stage of the microscope, and 

 6 



