ian genus _Iphidea_.

[Illustration: FIG. 20.--_Magellania [Waldheimia] flavescens_.
Logitudinal section with a portion of the animal.

d, h, Brachial appendages.
a, Adductor
c, c', Divaricator muscles.
s, Septum.
v, Mouth.
z, Exremity of alimentary tube. The penduncular muscules have been
purposely omitted.]

The body of the Brachiopod usually occupies about the posterior half of
the space within the shell. The anterior half of this space is lined by
the inner wall of the mantle and is called the mantle cavity. This
cavity lodges the arms, which are curved and coiled in different ways in
different genera. The water which bears the oxygen for respiration and
the minute organisms upon which the Brachiopod feeds is swept into the
mantle cavity by the action of the cilia which cover the arms, and the
eggs and excreta pass out into the same cavity. The mouth lies in the
centre of the anterior wall of the body. Its two lips fusing together at
the corners of the mouth are prolonged into the so-called arms. These
arms, which together form the lophophore, may be, as in _Cistella_,
applied flat to the inner surface of the dorsal mantle fold, but more
usually they are raised free from the body like a pair of moustaches,
and as they are usually far too long to lie straight in the mantle
cavity, they are folded or coiled up. The brachial skeleton which in
many cases supports the arms has been mentioned above.

[Illustration: FIG. 21.--A diagram of the left half of an _Argiope_
(_Megathyris_), which has been bisected in the median plane.

1. The ventral valve.
2. The dorsal valve.
3. The pedicle.
4. The mouth.
5. Lip which overhangs the mouth and runs all round the lophophore.
6. Tentacles.
7. Ovary in dorsal valve.
8. Liver diverticula.
9. Occlusor muscle--its double origin is shown.
10. Internal opening of left nephridium.
11. External opening of the same.
12. Ventral adjustor.
13. Divaricator muscle.
14. Sub-oesophageal nerve ganglion.
15. The heart.
16. Dorsal adjustor muscle.]

A transverse section through the arm (fig. 22) shows that it consists of
a stout base, composed of a very hyaline connective tissue not uncommon
in the tissues of the Brachiopoda, which is traversed by certain canals
whose nature is considered below under the section (_The Body Cavity_)
devoted to the coelom. Anteriorly this base supports a gurrie or gutter,
the pre-oral rim of