on consists of two quite distinct ganglia,
elongated in the longitudinal axis of the body, and separated from each
other by the whole width of the mouth; the chord which unites them is of
the same thickness as the rest of the collar. In all the genera, from
the front of each of the two supra-oesophageal ganglia, a pair of
nerves, (_f_, _f_,) united and together as large as the collar nerve,
rises, and can be traced running unbranched, in a nearly straight line,
for a length equalling the whole rest of the nervous chord, so as to
supply the peduncle and the inside of the capitulum or sack. At the
inner ends of these two same ganglia, from a central point where they
are united, a little central branch runs in front to the adductor
scutorum and other adjoining muscles; and still smaller fibrils run
behind to the oesophageal muscles.

[Illustration: Diagram of the anterior portion of the nervous system in
_Lepas fascicularis_. A. First thoracic or infra-oesophageal ganglion.
B. Second thoracic. C. Third thoracic ganglion. D. Supra-oesophageal
ganglion. E. The two ophthalmic ganglia. F. Double eye. _a_. Nerve going
to first cirrus; _b_, to the muscles below the first cirrus; _c_, to the
second cirrus; _d_, to the third; _e_, nerves running to the ovaria;
_f_, double nerves supplying the sack and peduncle.]

_Ophthalmic Ganglia and Eyes._--Owing to Professor Leidy's[16] discovery
of eyes in a Balanus, I was led to look for them in the Lepadidae.
Extending from the front of the two supra-oesophageal ganglia, two
chords may be seen in _Lepas fascicularis_ (of which a rude diagram is
here given), to run into two small, perfectly distinct oval ganglia
(E), which are not united by any transverse commissure. From the
opposite ends of these two ganglia smaller nerves run, and, bending
inwards at right angles, enter, beyond the middle, an elongated (F),
almost black, eye, composed of two eyes united together. Although in
outline the eye appears single, two lenses can be distinctly seen at the
end, directed upwards and towards the ganglia; two pigment-capsules can
also be distinguished; these are deep and cup-formed, and of a dark
reddish-purple. The following measurements will show the proportions of
the parts in a specimen of the _Lepas fascicularis_ having a capitulum
4/10ths of an inch in length.

Double eye { length 26/6000
{ width 13/6000

Diameter of single l