epresent a stomach, whether it is the simple
sac of the Polyps, or the cavity of the Acalephs, with its radiating
tubes traversing the gelatinous mass of the body, or the cavity and
tubes of the Echinoderms, inclosed within walls of their own.

The Mollusks represent circulation; and his division of this type into
classes, according to what he considers the higher or lower organization
of the heart, agrees with the ordinary division into Acephala,
Gasteropoda, and Cephalopoda.

The Articulates are the respiratory animals in this classification: they
represent respiration. The Worms, breathing, as he asserts, through the
whole surface of the skin, without special breathing organs, are the
lowest; the Crustacea, with gills, or aquatic breathing organs, come
next; and he places the Insects highest, with their branching tracheae,
admitting air to all parts of the body. The Vertebrates, or Flesh
Animals, with their four classes, represent the Bones, the Muscles, the
Nerves, and the Organs of Sense.

This theory, according to which there are as many great divisions as
there are structural systems or combinations of systems in the Animal
Kingdom, seemed natural and significant, and there was something
attractive in the idea that man represents, as it were, the synthetic
combination of all these different systems. Oken also, in his exposition
of his mode of classification, showed an insight into the structure and
relations of animals that commended it to the interest of all students
of Nature, and entitles him to their everlasting gratitude.
Nevertheless, his theory fails, when it is compared with facts. For
instance, there are many Worms that have no respiration through the
skin, while his appreciation of the whole class is founded on that
feature; and in his type representing circulation, the Mollusks, there
are those that have no heart at all. It would carry me too far into
scientific details, were I to explain all the points at which this
celebrated classification fails. Suffice it to say that there is no
better proof of the discrepancy between the system and the facts than
the constant changes in the different editions of Oken's own works and
in the publications of his followers founded upon his views, showing
that they were themselves conscious of the shifting and unstable
character of their scientific ground.

VI.

What, then, is the relation of these larger groups to each other, if
they do not stand in a conne