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 wi