MATERIAL FOR STUDY. 
n 
for convenience. Watch carefully for the appearance 
of either brown or green hydras. 
They may be seen without a magnifying-glass. If 
only eggs are present, they may not hatch for months, 
Fig. 12.—Water-fleas and Cyclops ( magnified). 
but sometimes adult hydras are captured attached to 
duckweed or other objects. Have several jars, and 
watch them all. Look for the appearance of buds on 
the sides of the hydras. Minute Crustacea (water-fleas 
and Cyclops) may appear in some of the jars. These 
are good food for hydras, and themselves furnish pleas¬ 
ing objects for study, both with and without the micro¬ 
scope. If either Crustacea or hydras appear, notice 
whether they prefer the light or the dark side of the 
jar. Add water only to replace that lost by evapora¬ 
tion. 
Some Water-breathing Insects. While collecting 
the hydras, look for objects that appear like moving 
sticks, or small moving rolls made of bits of leaves or 
pieces of sand. These are the larvae of caddis-flies. 
Watch them feed, and add material to the tubes which 
protect their delicate bodies. Keep plenty of plants 
about them. Larvae of other insects may be collected 
