ain of rings. If the student wants a perfect figure of metameric
segmentation he should think of a train of precisely similar
carriages, or a string of beads. One bead, one carriage, one
vertebra, would be a metamere.

Section 144. In contrast to metameric segmentation is the antimeric
repetition of radial symmetry (Section 142), in which each ray of the
star is called an antimere. It is possible to have bilateral symmetry
without a metameric arrangement of parts, as in the mussel and the
cuttle-fish; but metameric segmentation without complete or reduced
bilateral symmetry does not occur.

Section 145. We are now in a position to appreciate the fact that the
old and more popularly know division of animals into vertebrata and
invertebrata scarcely represents the facts of the case, that the
primary division should be into protozoa and metazoa, and that the
vertebrata are one of several groups of metazoa with a fundamental
bilateral symmetry and imperfect metameric segmentation.

The rabbit is one of the vertebrata, and, in common with all the other
animals collected under this head, it has--

(a) A skeletal axis (the vertebral column) between its central
nervous system and its body cavity. In the adult rabbit this
consists of a chain of vertebrae, but in the embryo (i.e., the
young rabbit before birth) it is represented by a continuous chord,
the notochord, and it remains as such in some of the lowest
vertebrata throughout life. In other words, in these lower
vertebrata, the vertebral axis is not metameric.

(b) A dorsal and -Tubular_ nervous axis. (Section 131, the central
canal)

(c) It has, though in the embryo only, certain slits between the
throat and the exterior, like the gill slits of a fish. Such
slits are-- with one or two remarkable exceptions outside the
sub-kingdom-- distinctly vertebrate features, and remain, of course,
in fishes throughout life.

The presence of true cartilage and bone mark a vertebrate, but
vertebrata occur in which -these tissues- [bone] -are- [is] absent.

Section 146. The rabbit shares the following features with all the
vertebrata, except the true fishes, which do not possess any of them--

(a) Lungs (but many fish have a swimming bladder which answers
to the lungs in its anatomical relations.)

(b) Limbs which consist of a proximal joint of one bone an
intermediate part of two, and a distal portion which has five