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. [Illustration: Fig. 7. LARVÆ OF THE GNAT in two different stages of development (Magnified).] [Illustration: Fig. 8. CYCLOPS _a_ large antennæ; _b_ smaller do.; _c_ egg-sacs (Magnified).] [Illustration: Fig. 9. DAPHNIA: _a_ pulsatile sac, or heart; _b_ eggs; _c_ digestive tube (Magnified).] Observe, also, those grotesque _Entomostraca_,[17] popularly called “water-fleas,” although, as you perceive, they have little resemblance in form or manners to our familiar (somewhat _too_ familiar) bedfellows. This (Fig. 8) is a _Cyclops_, with only one eye in the centre of its forehead, and carrying two sacs, filled with eggs, like panniers. You observe he has no legs; or, rather, legs and arms are hoisted up to the head, and become antennæ (or feelers). Here (Fig. 9) is a _Daphnia_, grotesque enough, throwing up his arms in astonished awkwardness, and keeping his legs actively at work inside the shell--as respirators, in fact. Here (Fig. 10) is an _Eurycercus_, less grotesque, and with a much smaller eye. Talking of eyes, there is one of these Entomostraca named _Polyphemus_, whose head is all eye; and another, named _Caligus_, who has no head at all. Other paradoxes and wonders are presented by this interesting group of animals;[18] but they all sink into insignificance beside the paradox of the amazonian entomostracon, the _Apus_--a race which dispenses with masculine services altogether, a race of which there are no males! [Illustration: Fig. 10. EURYCERCUS: _a_ heart; _b_ eggs; _c_ digestive tube (Magnified).]