Here is a pond with a mantling surface of green promise. Dip the jar into the water. Hold it now up to the light, and you will see an immense variety of tiny animals swimming about. Some are large enough to be recognized at once; others require a pocket-lens, unless familiarity has already enabled you to infer the forms you cannot distinctly see. Here ([Fig. 7]) are two larvæ (or grubs) of the common gnat. That large-headed fellow (A) bobbing about with such grotesque movements, is very near the last stage of his metamorphosis; and to-morrow, or the next day, you may see him cast aside this mask (larva means a mask), and emerge a perfect insect. The other (B) is in a much less matured condition, but leads an active predatory life, jerking through the water, and fastening to the stems of weed or sides of the jar by means of the tiny hooks at the end of its tail. The hairy appendage forming the angle is not another tail, but a breathing apparatus.
Fig. 7.
Larvæ of the Gnat in two different stages of development (Magnified).
Fig. 8.
Cyclops
a large antennæ;
b smaller do.;
c egg-sacs (Magnified).
Fig. 9.
Daphnia: a pulsatile sac, or heart;
b eggs;
c digestive tube (Magnified).