Descjiption of a Species of Caligus. 243 



sertion of the more powerful of the abdominal muscles below the 

 centre of this segment, in preference to an attachment near its 

 base, enables the animal to give this segment great flexion. When 

 the animal has been attached to the glass out of the water, we 

 have often separated the anterior portion of the body from the 

 glass, till it formed an angle of 75° or 80° with the abdominal 

 portion, and generally the animal has succeeded through the ac- 

 tion of these muscles in restoring its head again to the glass. 



The muscle (O) on the back may possibly be attached to the 

 muscle (N) and not to the thoracic segment. We have not sue- 

 ceeded, in our dissections, in exposing these muscles in order to 

 determine this point. 



b. Muscles of the organs appertaining to the several segments. 



1. Anterior Cephalic Segment. — In the following account, we 

 shall in general describe only the muscles moving the basal 

 joints of each of the legs. More minute particulars may be ob- 

 tained by reference to the plates. 



The muscles moving the cup, have not been satisfactorily de- 

 termined. A slightly elevated line passes from each side with a 

 curve into the membrane of this organ, which may be muscular ; 

 if so, they act in flattening the cup preparatory to its attachment. 



The antennas have two extensors and one flexor. The two ex- 

 tensors are inserted in a tendon, occupying the anterior margin of 

 the base. They extend half way to the eyes ; one (a, fig. 7 and 

 fig. 1) above the flexor of the anterior cephalic segment, is 

 attached to the upper shell ; the other, (a', fig. 1,) much the small- 

 est, passing under the same muscle, is attached below. The 

 flexor (b, figs. 7 and 1,) is inserted near the outer part of the base, 

 by means of a short tendon, and is attached near the base of the 

 preceding muscles. These organs have but little motion, and are 

 seldom observed in action. 



2. Posterior Cephalic Segment. — The elevators of the buccal 

 mass are four short narrow muscles, inserted in the bony pro- 

 cesses, g, (figs. 12 or 17,) and attached to the teguments below, 

 under the anterior extremity of the mouth ; the insertion of one is 

 exactly posterior, and of the other, a little lateral, as is represented 

 in fig. 17. By means of these muscles the buccal mass may be 

 elevated to a right angle with the surrounding parts. On dying, 

 the mouth is often left in this elevated position. A muscular 

 band passes across the back part of the buccal mass and after 



