To the best of our knowledge the Age of Man is but a paltry fifty thousand years. Behind this the Age of Mammals may have numbered three millions; then back of these came the Age of Reptiles with more than seven millions of years, during all of which time the tentacles of unnumbered generations of Bryozoans waved in the sea. Back, back farther still we add another seven million years, or thereabouts, of the Age of the Amphibians, when the coal plants grew, and the Age of the Fishes. And finally, beyond all exact human calculation, but estimated at some five million, we reach the Age of Invertebrates in the Silurian, and in the lowest of these rocks we find beautifully preserved fossils of Bryozoans, to all appearances as perfect in detail of structure as these which we have before us to-day in this twentieth century of man's brief reckoning. These tiny bits of jelly are transfigured as well by the grandeur of their unchanged lineage as by the appearance of the little animals from within. What heraldry can commemorate the beginning of their race over twenty millions of years in the past! The student of mythology will feel at home when identifying some of the commonest objects of the pond. And most are well named, too, as for instance the Hydra, a small tube-shaped creature with a row of active tentacles at one end. Death seems far from this organism, which is closely related to the sea-anemones and corals, for though a very brief drying will serve to kill it, yet it can be sliced and cut as finely as possible and each bit, true to its name, will at once proceed to grow a new head and tentacles complete, becoming a perfect animal. Then we shall often come across a queer creature with two oar-like feelers near the head and a double tail tipped with long hairs, while in the centre of the head is a large, shining eye,--Cyclops he is rightly called. Although so small that we can make out little of his structure without the aid of the lens, yet Cyclops is far from being related to the other still smaller beings which swim about him, many of which consist of but one cell and are popularly known as animalculae, more correctly as Protozoans. Cyclops has a jointed body and in many other ways shows his relationship to crabs and lobsters, even though they are many times larger and live in salt water. Another member of this group is Daphnia, although the appropriateness of this name yet remains to be discovered; Daphnia being a chunky-bodied little being, with a double-branched pair of oar-like appendages, with which he darts swiftly through the water. Although covered with a hard crust like a crab, this is so transparent that we can see right through his body. The dark mass of food in the stomach and the beating heart are perfectly distinct. Often, near the upper part of the body, several large eggs are seen in a sort of pouch, where they are kept until hatched.