e small
end. At the point which answers to that from which the two cilia arise in
_Heteromita_, there is a conical depression, the mouth; and, in young
specimens, a tapering filament, which reminds one of the posterior cilium
of _Heteromita_, projects from this region.

The body consists of a soft granular protoplasmic substance, the middle
of which is occupied by a large oval mass called the "nucleus"; while, at
its hinder end, is a "contractile vacuole," conspicuous by its regular
rhythmic appearances and disappearances. Obviously, although the
_Colpoda_ is not a monad, it differs from one only in subordinate
details. Moreover, under certain conditions, it becomes quiescent,
incloses itself in a delicate case or _cyst_, and then divides into two,
four, or more portions, which are eventually set free and swim about as
active _Colpodoe_.

But this creature is an unmistakable animal, and full-sized _Colpodoe_
may be fed as easily as one feeds chickens. It is only needful to diffuse
very finely ground carmine through the water in which they live, and, in
a very short time, the bodies of the _Colpodoe_ are stuffed with the
deeply-coloured granules of the pigment.

And if this were not sufficient evidence of the animality of _Colpoda_,
there comes the fact that it is even more similar to another well-known
animalcule, _Paramoecium_, than it is to a monad. But _Paramoecium_ is so
huge a creature compared with those hitherto discussed--it reaches 1/120
of an inch or more in length--that there is no difficulty in making out
its organisation in detail; and in proving that it is not only an animal,
but that it is an animal which possesses a somewhat complicated
organisation. For example, the surface layer of its body is different in
structure from the deeper parts. There are two contractile vacuoles, from
each of which radiates a system of vessel-like canals; and not only is
there a conical depression continuous with a tube, which serve as mouth
and gullet, but the food ingested takes a definite course, and refuse is
rejected from a definite region. Nothing is easier than to feed these
animals, and to watch the particles of indigo or carmine accumulate at
the lower end of the gullet. From this they gradually project, surrounded
by a ball of water, which at length passes with a jerk, oddly simulating
a gulp, into the pulpy central substance of the body, there to circulate
up one side and down the other, until its contents are d