248 Description of a Species of Caligus. 
of the remaining two, (x,) arises just above the posterior sinus, 
and the other from the inner margin of this sinus; both are at- 
tached on the back, and inserted near the ai tieti dion of the ster- 
num. The flexor muscles arise below, just outside the apron, and 
occupy the greater part of its interior. A single muscle is attached 
near the articulation of the sternum, and passes into the basal 
portion. 
This apron, appended to the cephalo-thoracic segment, forms 
the anterior portion of the body into a large, broad cup, which is 
perfectly closed, with the exception of a small opening at each of 
the posterior sinuses. 'These we have already described as pro- 
vided with a folded membrane, furnished with muscles capable of 
drawing it over and completely shutting the opening. The mem- 
branous margin of the animal near the antenne, has also a fold 
by which a small leak, if it be such, is closed. Considering these 
several provisions, it is probable, that the whole of this anterior 
portion of the animal is especially adapted to enable the animal 
to attach itself firmly during the rapid motions of the fish, and 
that the small marginal cups in front are relied on, only while the 
fish is stationary, or but slowly moving. 
. The remaining pair of legs are moved by short slender muscles, 
and seem to possess little power. They usually hang loose and 
motionless while the animal is swimming, and when attached to 
the body of the fish, are commonly extended by the side of the 
abdomen. 
| Ill. Nervous System. 
a. The organs of the senses. 
The only organs in the Caligus, which we have been able to 
distinguish as the undoubted residence of special senses, are the 
eyes and the antenne. The latter organs have already been de- 
seribed ; it remains to explain the structure of the eyes. 
The eyes are wholly internal, and are situated near the centre 
of the posterior cephalic segment, directly over the lower part of 
the buccal mass. They are two in number, simple in their struc- 
ture, and placed near one another, on a single ‘teddish-black ground. 
They project from each side of this colored ground, with a spher- 
ical surface, somewhat exceeding a hemisphere. : On dissection 
adily distinguis a “igs 
AD ‘Kaine , which is p nd forms the sph 
ical surface of the eye: 
