points (_b_), generally rather more than the
1/1000th of an inch in length; they are rather variable in size, and
seem to be of no functional importance; directly beneath them, there
are four little calcareous beads (as may be known by their dissolving
with effervescence in any acid, and breaking easily under the needle);
these are the 3/2000ths of an inch in their larger external diameter;
they are rather deeply imbedded in the outer integument, and taper a
little downwards ending in a concave terminal point, into which a minute
tubulus enters, like those passing into and through the valves of
ordinary Cirripedia: along the axis of imbedment, they are often
4/2000ths of an inch in length. These calcareous beads or rudimental
valves are seated in pairs, at the two ends of the flattened animal, so
that when the animal is laid on one side, the upper bead in each pair
exactly covers and hides the lower one. The outer integument is composed
of chitine, as may be inferred from boiling caustic potash having no
effect on it; the upper part is thicker than the imbedded portion and is
wrinkled transversely; it is covered with minute spines 4/10,000ths of
an inch in length, either single or in groups of two and three, (Pl. V,
fig. 14.) This outer tunic is lined by corium, sometimes slightly
mottled with dull purple; and this by delicate, longitudinal, striae-less
muscles, running from the base up to the under edge of the orifice;
these longitudinal muscles are crossed, at least, in the upper part, by
still finer transverse muscles.

_Thorax and Abdomen._--When the external integument is cut open, the
thorax (Pl. V, fig. 13) is found lodged within an inner sack or rather
tube, extending from near the bottom of the animal, up to the external
orifice. The whole thorax is sometimes forced through the orifice, owing
perhaps to the action of the spirits of wine and consequent endosmose,
and is thus well displayed without dissection. The thorax tapers a
little, is much flattened and straight; its length, together with the
terminal abdominal lobe, is about 6/400ths of an inch; it is formed of
very thin, most finely hirsute membrane, transversely wrinkled and so
extensible, that when everted by the internal muscles being seized, it
stretches to twice its former length; in this condition, five transverse
articulations are displayed. The abdominal lobe is smooth, and cannot
be stretched, or turned inside out by pulling the above muscles. On