ree) other thoracic ganglia, when
viewed as transparent bodies, are seen to be solid; but in some of the
genera, as in Conchoderma, the outline plainly shows, that each consists
of a lateral pair fused together. The second thoracic ganglion (B) is
rather small; it is either close to the first, as in _Pollicipes
mitella_ and _Lepas fascicularis_, or far distant, as in Ibla. The third
(C) and fourth are of about the same size with the second: these three
ganglia send large branches to the second, third, and fourth pair of
cirri: other minute branches spring from their under sides, and from the
intermediate double chords. The fifth ganglion is larger and longer than
the three preceding ones, and gives off nerves to the fifth and sixth
pair of cirri; it is clearly formed by the union of the fifth, with what
ought to have formed a sixth ganglion. The two nerves going to the sixth
cirrus give off on their inner sides, each a great branch to the penis.
In _Pollicipes mitella_, in which there are only four instead of five
thoracic ganglia, it is evident from the outline and position of the
nerves going to the fourth pair of cirri, that the fourth ganglion is
fused into the fifth, itself, as we have just seen, normally composed of
two consecutive ganglia. In this Pollicipes there is other evidence of
concentration in the nervous system, for none of the ganglia show signs
of being formed of lateral pairs; the second is close to the first; and
the abdominal double chord is in part separated by a mere cleft; lastly,
as we shall immediately see, the same remark is applicable to the
supra-oesophageal ganglia.

The latter (D) alone remain to be described; they present far more
diversity in shape than do the thoracic ganglia; they are almost always
seen in outline to be laterally distinct, and usually resemble two pears
with their tapering ends cut off and united; in a transverse line they
are as long as the infra-oesophageal ganglion, but are much less
massive. In _Lepas fascicularis_ (D), they are pear-shaped; in
_Pollicipes mitella_ they are globular, and separated by a third
globular ganglion, which I believe is the ophthalmic ganglion, presently
to be described; in _Pollicipes spinosus_, however, the ophthalmic
ganglion is, as usual, placed in advance of the supra-oesophageal
ganglion, which latter, in this one species, shows no sign of being
formed of a lateral pair fused together. In _Alepas cornuta_ the
supra-oesophageal gangli