the rabbit, and in most other
types, in various organs, we find ciliated epithelium (Figure VII.).
This is columnar or cubical in form, and with the free edge curiously
modified and beset with a number of hair-like processes, the cilia, by
which, during the life of the cell, a waving motion is sustained in one
direction. This motion assists in maintaining a current in the contents
of ducts which are lined with this tissue. The motion is independent of
the general life of the animal, so long as the constituent cell still
lives, and so it is easy for the student to witness it himself with a
microscope having a 1/4-inch or 1/6-inch objective. Very fine cilia may
be seen by gently scraping the roof of a frog's mouth (the cells figured
are from this source), or the gill of a recently killed mussel, and
mounting at once in water, or, better, in a very weak solution of
common salt.

Section 60. The lining of glands is secretory epithelium; the cells
are usually cubical or polygonal (8, g.ep.), and they display in the
most characteristic form what is called metabolism. Anaboly (see
Section 14) we have defined, as a chemical change in an upward
direction-- less stable and more complex compounds are built up in
the processes of vegetable and animal activity towards protoplasm;
kataboly is a chemical running down; metaboly is a more general
term, covering all vital chemical changes. The products of the action
of a glandular epithelium are metabolic products, material derived from
the blood is worked, up within the cell, not necessarily with
conspicuous gain or loss of energy, and discharged into the gland
space. The most striking case of this action is in the "goblet cells"
that are found among the villi; these are simply glands of one cell,
unicellular glands, and in Figure V. we see three stages in their
action: at g.c.1 material (secretion) is seen forming in the cell, at
g.c.2 it approaches the outer border, and at g.c.3 it has been
discharged, leaving a hollowed cell. Usually however, the escape of
secreted matter is not so conspicuous, and the gland-cells are
collected as the lining of pits, simple, as in the gastric, pyloric, and
Lieberkuhnian glands (Figure VIII., Sections 23, 29), or branching
like a tree or a bunch of grapes (Figure r.g.), as in Brunner's glands
(Section 29) the pancreas, and the salivary glands. The salivary
glands, we may mention, are a pair internal to the posterior ventral
angle of the jaw, the s