Turning then to the diagram (Fig. 6) I will describe it as I hope you will see it under the microscope—­a curious, tiny, perfectly transparent open-mouthed vase standing upright on the weed, and having an equally transparent being rising up in it and waving its tiny lashes in the water.  This is really all one animal, the vase hc being the horny covering or carapace of the body, which last stands up like a tube in the centre.  If you watch carefully, you may even see the minute atoms of food twisting round inside the tube until they are digested, after they have been swept in at the wide open mouth by the whirling lashes.  You will see this more clearly if you put a little rice-flour, very minutely powdered and colored by carmine, into the water; for you can trace these red atoms into some round spaces called vacuoles which are dotted over the body of the animal, and are really globules of watery fluid in which the food is probably partly digested.

You will notice, however, one round clear space (cv) into which they do not go, and after a time you will be able to observe that this round spot closes up or contracts very quickly, and then expands again very slowly.  As it expands it fills with a clear fluid, and naturalists have not yet decided exactly what work it does.  It may serve the animal either for breathing, or as a very simple heart, making the fluids circulate in the tube.  The next interesting point about this little being is the way it retreats into its sheltering vase.  Even while you are watching, it is quite likely it may all at once draw itself down to the bottom as in No. 2, and folding down the valves w of horny teeth which grow on each side, shut itself in from some fancied danger.  Another very curious point is that, besides sending forth young ones, these creatures multiply by dividing in two (see No. 3, Fig. 6), each one closing its own part of the vase into a new home.

There are hundreds of these Infusoria, as they are called, in my pond, some with vases, some without, some fixed to weeds and stones, others swimming about freely.  Even in the water-trough in which this Thuricolla stands, I saw several smaller forms, and the next microscope has a trough filled with the minutest form of all, called a Monad.  These are so small that two thousand of them could lie side by side in an inch; that is, if you could make them lie at all, for they are the most restless little beings, darting hither and thither, scarcely even halting except to turn back.  And yet though there are so many of them, and as far as we know they have no organs of sight, they never run up against each other, but glide past more cleverly than any clear-sighted fish.  These creatures are mostly to be found among decaying seaweed, and though they are so tiny, you can still see distinctly the clear space contracting and expanding within them.

[Illustration:  FIG. 7.  LIVING DIATOMS.

a, Cocconema lanceolatum. b, Bacillaria paradoxa. c, Gomphonema marinum. d, Diatoma hyalina.]