s: as
Burmeister has shown, there are also two channels in the penis. There
are two dorso-lateral channels in the prosoma, which are in direct
connection with the great main channel, running down the rostral (_i.
e._, ventral) side of the peduncle. This latter main channel branches
out in the lower part, and transmits the fluid through the ovarian
tubes, whence, I believe, it flows upwards and round the sack,
re-entering the body near the sides of the adductor scutorum muscle. The
main rostral channel (or artery?) in the uppermost part of the peduncle,
has a depending curtain, which, I think, must act as a valve, so as to
prevent the circulating fluid regurgitating into the animal's body
during the contractions of the peduncle.

_Nervous System and Organs of Sense._--In most of the genera, there are
six _main_ ganglia, namely, the supra-oesophageal, and five thoracic
ganglia; but in _Pollicipes mitella_ there are only four thoracic
ganglia. Of these, the first thoracic or infra-oesophageal ganglion is
considerably the largest and most massive; it is squarish, or oval, or
heart-shaped; it presents no trace of being formed by the union of two
lateral ganglia. Two great nerves spring from its under side (A),
represented in the woodcut on page 49, by dotted lines, and run straight
down amongst the viscera in the prosoma: these nerves are about as large
as those forming the collar and those running to the second ganglion;
hence, six great nerves meet here, two in front, two behind, and two on
the under side. At the anterior end, over the junction with the collar
chord, three equal-sized nerves rise on each side, with a fourth,
smaller one, outside; these go to the trophi and to the two olfactory
sacks. At the posterior end, on each side, a pair of nerves branch out
rectangularly, one of which (_a_,) goes to the first cirrus, and there
divides into two branches; of these, the upper runs up the cirrus, and
the lower one downwards. The other nerve (_b_), proceeding on each side
from this first thoracic ganglion, runs to the muscles beneath the basal
articulation of the first cirrus. The collar surrounding the oesophagus
is generally very long, sometimes equalling the whole thoracic chord; at
a middle point, a small branch is sent off, and at the anterior end
(_e_, _e_), close to the supra-oesophageal ganglia, double or treble
fine branches run to the true ovaria, lying close to the upper end of
the stomach. The four (or only th