e and capitulum in the
Lepadidae, as the nerves of the ophthalmic ganglia go exclusively to the
eyes. Finally, I may remark that in Pollicipes, looking to the whole
nervous system, the state of concentration nearly equals that in certain
macrourous decapod crustaceans, for instance the _Astacus marinus_, of
which a figure is given by Milne Edwards.

_Olfactory Organs._--In the outer maxillae, at their bases where united
together, but above the basal fold separating the mouth from the body,
there are, in all the genera, a pair of orifices (Pl. X, fig. 16); these
are sometimes seated on a slight prominence, as in Lithotrya, or on the
summit of flattened tubes (Pl. X, fig. 17), projecting upwards and
towards each other, as in Ibla, Scalpellum, and Pollicipes. In Ibla
these tubular projections rise from almost between the outer and inner
maxillae. It is impossible to behold these organs, and doubt that they
are of high functional importance to the animal. The orifice leads into
a deep sack lined by pulpy corium, and closed at the bottom. The outer
integument is inflected inwards, (hence periodically moulted,) and
becoming of excessive tenuity, runs to near the bottom of the sack,
where it ends in an open tube: so excessively thin is this inflected
membrane, that, until examining Anelasma, I was not quite certain that I
was right in believing that the outer integument did not extend over the
whole bottom. I several times saw a nerve of considerable size entering
and blending into a pulpy layer at the bottom of the sack of corium; but
I failed in tracing to which of the three pair of nerves, springing from
the front end of the infra-oesophageal ganglion, it joined. I can hardly
avoid concluding, that this _closed_ sack, with its naked bottom, is an
organ of sense; and, considering that the outer maxillae serve to carry
the prey entangled by the cirri towards the maxillae and mandibles, the
position seems so admirably adapted for an olfactory organ, whereby the
animal could at once perceive the nature of any floating object thus
caught, that I have ventured provisionally to designate the two orifices
and sacks as olfactory.

_Acoustic_ (?) _Organs._--A little way beneath the basal articulation of
the first cirrus (Pl. IX, fig. 4 _d_, and Pl. IV, fig. 2 _e_), on each
side, there may be seen a slight swelling, and on the under side of
this, a transverse slit-like orifice, 1/20th of an inch in length in
Conchoderma, but often on