Description of a Species of Caligus. 249 
2. A lens, simple, spherical, and distant from the cornea; its 
diameter is about half that of the cornea :* 
3. A colorless, transparent fluid, which we presume to be the 
aqueous humor, occupying the space just within the cornea: 
4. A deep red, nearly black pigment, which forms the colored 
spot supporting the eyes. 
We have not observed the vitreous humor. In the spherical 
form of the lens, the eyes resemble the same organs in fishes. They 
are not movable, and have no connections except by the optic 
nerve. ‘The adjacent parts are transparent, enabling the animal 
to see in both directions. We have already described the shell - 
above, and referred to its representation in fig. 8, Pl. IV. It is 
perfectly flat, without any spherical projection, corresponding to 
that of the cornea within. The translucent elongated space in fig. 
8, lies in the shell, and passes over the space between the eyes. 
he nerves. 
The nervous system contains but two ganglions, and these by 
their close approximation appear at first, to compose but one. 
They are situated directly behind the eyes, the one above the 
esophagus, and the other below it, and are so intimately connect- 
ed on each side of this portion of the alimentary canal, that it has 
been found impossible to separate them, (fig. 20.) Indeed, it would 
scarcely convey an incorrect idea of the form, to describe it as a 
single mass, with a longitudinal cavity through the centre, for the 
passage of the esophagus. The size of the united ganglions is 
rather greater than that of the buccal mass. The nerves arising 
from these ganglions are flat, fibrous cords, enclosed within a 
membranous envelope or neurolemma. This neurolemma is often 
one fourth wider than the bundle of nervous fibres contained with- 
in, and these fibres appear to pass through without any attach- 
ment. The neurolemma is sometimes slightly folded, which 
gives acrenated appearance to the margin of the nerve. 
The brain or cephalic ganglion has a broad ovate or sub-cordate 
form. It gives off three pairs of nerves. 
The first pair, (a fig. 20, Pl. IV,) leaves the central part of the 
anterior margin and passes directly to the eyes. As the eyes are 
adjacent to the ganglion, these nerves are very short. 
_* The lens in the simple eyes of crustacea is usually described as being in im- 
mediate contact with the cornea: it was very evidently distant from this mem- 
brane, in the Caligus. 
Vou. XXXIV.—No. 2. 32 
