ens 6/6000

Ophthalmic ganglion { length 16/6000
{ breadth 11/6000

Supra-oesophageal ganglion, }
transverse or longest axis } 126/6000
of both together }

Supra-oesophageal ganglion, }
longitudinal axis of } 45/6000

Infra-oesophageal ganglion, }
transverse axis of } 120/6000

Infra-oesophageal ganglion, }
longitudinal axis of } 114/6000

[16] Proceedings of the Academy of Natural Sciences,
Philadelphia. No. i, vol. iv, Jan. 1848.

In _Conchoderma aurita_ the ophthalmic ganglia are much smaller, and
nearer to the supra-oesophageal ganglion, than in _L. fascicularis_. In
_Alepas cornuta_ the ophthalmic chords run towards each other from the
two distant and separate supra-oesophageal ganglia; and the ophthalmic
ganglia, (instead of being quite separate, as in _L. fascicularis_,) are
united by their front ends, and the two eyes instead of standing some
way in front, with nerves running to them, are embedded on the double
ophthalmic ganglion; the pigment-capsules here, also, have the shape of
mere saucers, and are joined back to back, with the two lenses
projecting far out of them. In neither sex of Ibla could I perceive that
the eye was double. In _Pollicipes spinosus_ the ophthalmic ganglion
stands in front of the single supra-oesophageal ganglion, and shows no
signs of being formed of a lateral pair; the eyes themselves, however,
differently from, in all the foregoing cases, are, though approximate,
quite distinct. In _Pollicipes mitella_ I did not see the eyes; but the
ophthalmic ganglion consists, as I believe, of a single globular one,
placed exactly between the two globular, supra-oesophageal ganglia, all
three being of nearly equal size. Professor Leidy does not mention the
ophthalmic ganglia; hence I infer that in Balanus, which is a more
highly organised Cirripede, they are fused into the supra-oesophageal
ganglion.

In all the genera, the double eye is seated deep within the body; it is
attached by fibrous tissue to the radiating muscles of the lowest part
of the oesophagus, and lies actually on the upper part of the stomach;
consequently, a ray of light, to reach the eye, has to pass through the
exterior membrane and underlying corium connecting the two scuta, and to
penetrate deeply into the body. In living sessile