250 Descriptioti 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 antennae 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 

 pair 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 an- 

 gles of the brain, and pass to the antennas ; they are one half lar- 

 ger than any other in the body. Near the origin, they give ofi" ex- 

 teriorly a slender branch, which continues nearly parallel with 

 the main nerve, and passes to the muscles of the antennae. With- 

 out farther branching they extend in nearly a straight line to the 

 base of the antennas, where they subdivide into four large branch- 

 es, which are distributed to the fleshy papillae, (fig. 19, PI. 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 setae. The antennae 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 papillee, appeair adapted. 



The thoracic ganglion, which is composed of all the thoracic 

 and abdominal ganglions united, has a cordate form, and is some- 

 what larger than the brain. Its inferior extremity extends rather 



