250 Description of a Species of Caligus. 
The second pair, (b fig. 20,) arises from the same margin later- 
ally, and extends upward towards the cup, (fig. 18,) passing just 
within the articulating process of the cephalic segments. It gives 
out large branches which are distributed to the surrounding mus- 
cles and teguments. The anterior extremity which goes to the 
cup is scarcely one third the size of the base. 
A small hollow vessel, (fig. 18,) extends from the organs which 
we have considered analogous to the inner antennz in other crus- 
tacea, along the median line, and appears to terminate in a bulb, 
about half way to the brain. This vessel has been the subject 
of much investigation, without removing all the doubts respecting 
its nature. When separated from the body, it appears to be a 
large neurolemma, containing two small bundles of nervous fibres, 
and this is our final conclusion, though adopted with some hesita- 
tion. It appears probable, from the result of some of our dissec- 
tions, that this bulb receives a nerve from each side, which either 
arises directly from the brain, or, is a branch of the nerve last de- 
scribed. If this is a distinct pair, it corresponds to the third, or 
inner antennary pair in the lobster, as given by Edwards, and the 
= described as passing to the cup, and surrounding teguments 
and muscles, is the analogue of the fourth pair, which has a simi- 
lar distribution in the lobster. 
The remaining pair of nerves, (c,) arise from the anterior all- 
gles of the brain, and pass to the antenne ; they are one half lar- 
ger than any other in the body. Near the origin, they give off ex- 
teriorly a slender branch, which continues nearly parallel with 
the main nerve, and passes to the muscles of the antennee. With- 
out farther branching they extend in nearly a straight line to the 
base of the antennz, where they subdivide into four large branch- 
es, which are distributed to the fleshy papilla, (fig. 19, Pl. V-) 
Two nerves from the posterior branch run along the muscles, and 
are continued into the terminal joints, one to each of the two ter- 
minating sets of sete. The antenne are so abundantly furnished 
with nerves, that they must be the seat of an important sense. 
The sense of touch is the only one for which their peculiar form, 
and their delicate papilla, appear adapted. 
The thoracic ganglion, which is new of all the thoracic 
_ganglions united, has a cordate form, and is some- 
what larger than the brain. Its inferior os extends rather 
