Here; look into this opening in the milfoil and crowfoot bed. Do you see a grey film around that sprig? Examine it through the pocket lens. It is a forest of glass bells, on branching stalks. They are Vorticellæ; and every one of those bells, by the ciliary current on its rim, is scavenging the water—till a tadpole comes by and scavenges it. How many millions of living creatures are there on that one sprig? Look here!—a brown polype, with long waving arms—a gigantic monster, actually a full half-inch long. He is _Hydra fusca_, most famous, and earliest described (I think by Trembley). Ere we go home I may show you perhaps _Hydra viridis_, with long pea-green arms; and _rosea_, most beautiful in form and colour of all the strange family. You see that lump, just where his stalk joins his bell-head? That is a budding baby. Ignorant of the joys and cares of wedlock, he increases by gemmation. See! here is another, with a full-sized young one growing on his back. You may tear it off if you will—he cares not. You may cut him into a dozen pieces, they say, and each one will grow, as a potato does. I suppose, however, that he also sends out of his mouth little free ova—medusoids—call them what you will, swimming by ciliæ, which afterwards, unless the water beetles stop them on the way, will settle down as stalked polypes, and in their turn practise some mystery of Owenian parthenogenesis, or Steenstruppian alternation of generations, in which all traditional distinctions of plant and animal, male and female, are laughed to scorn by the magnificent fecundity of the Divine imaginations. That dusty cloud which shakes off in the water as you move the weed, under the microscope would be one mass of exquisite forms—Desmidiæ and Diatomaceæ, and what not? Instead of running over long names, take home a little in a bottle, put it under your microscope, and if you think good verify the species from Hassall, Ehrenberg, or other wise book; but without doing that, one glance through the lens will show you why the chalk trout grow fat. Do they, then, eat these infusoria? That is not clear. But minnows and small fry eat them by millions; and so do tadpoles, and perhaps caddis baits and water crickets. What are they?