Visit to the ponds--Confervæ--Spirogyra quinina--Vorticella--Common Rotifer--Three divisions of Infusoria--Phytozoa--Protozoa--Rotifera--Tardigrada--Meaning of these terms--Euglenæ--Distinction between animals and vegetables--Description of Vorticellæ--Dark ground illumination--Modes of producing it--The Nucleus of the Vorticellæ--Methods of reproduction--Ciliated Protozoa--Wheel bearers or Rotifers--Their structure--The common Rotifer--The young Rotifer seen inside the old one--An internal nursery--"Differentiation" and "Specialisation"--Bisexuality of Rotifers--Their zoological position--Diversities in their appearance--Structure of their Gizzard--Description of Rotifers. The winter months are on the whole less favorable to the collection of microscopic objects from ponds and streams than the warmer portions of the year; but the difference is rather in abundance than in variety, and with a very moderate amount of trouble, representatives of the principal classes can always be obtained. On a clear January morning, when the air was keen, but no ice had yet skinned over the surface of the water, a visit to some small ponds in an open field not far from Kentish Town provided entertainment for several days. The ponds were selected from their open airy situation, the general clearness of their water, and the abundance of vegetation with which they were adorned. Near the margin confervæ abounded, their tangled masses of hair-like filaments often matted together, almost with the closeness of a felted texture. At intervals, minute bubbles of air, with occasionally a few of greater size, indicated that the complex processes of vegetable life were actively going on, that the tiny plants were decomposing carbonic acid, dexterously combining the carbon--which we are most familiar with in the black opaque form of charcoal--to form the substance of their delicate translucent tissues, and sending forth the oxygen as their contribution to the purification of the adjacent water, and the renovation of our atmospheric air. This was a good sign, for healthy vegetation is favorable to many of the most interesting forms of infusorial life. Accordingly the end of a walking-stick was inserted among the green threads, and a skein of them drawn up, dank, dripping, and clinging together in a pasty-looking mass. To hold up a morsel of this mass, and tell some one not in the secrets of pond-lore that its dripping threads were objects of beauty, surpassing human productions, in brilliant colour and elegant form, would provoke laughter, and suggest the notion that you were poking fun at them, when you poked out your stick with the slimy treasure at its end. But let us put the green stuff into a bottle, with some water from its native haunt, cork it up tight, and carry it away for quiet examination under the microscope at home.