Some (the Flagellates) have one or two stout oars;
some (the Ciliates) have numbers of fine hairs (or cilia). Some
have a definite mouth-funnel, but no stomach, and cilia drawing
the water into it. Some (Vorticella, etc.), shrinking from the
open battlefield, return to the plant-principle, live on stalks,
and have wreaths of cilia round the open mouth drawing the water
to them. Some (the Heliozoa) remain almost motionless, shooting
out sticky rays of their matter on every side to catch the food.
Some form tubes to live in; some (Coleps) develop horny plates
for armour; and others develop projectiles to pierce their prey
(stinging threads).
This miniature world is full of evolutionary interest, but it is
too vast for detailed study here. We will take one group, which
we know to have been already developed in the Cambrian, and let a
study of its development stand for all. In every lecture or book
on "the beauties of the microscope" we find, and are generally
greatly puzzled by, minute shells of remarkable grace and beauty
that are formed by some of these very elementary animals They are
the Radiolaria (with flinty shells, as a rule) and the
Thalamophora (with chalk frames).
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