Description of a Species of Caligus. 253 



interiorly, which passes down the venter, and appears to be dis- 

 tributed to the ventral muscles. As they approach this pair of 

 natatories, they give off another branch from the same side, which 

 also passes backward, and is supposed to furnish nerves to the pos- 

 terior muscles of these legs. On entering these natatories, the 

 nerve divides into two branches, the upper of which soon gives 

 off a third ; the inner nerve, as in the preceding legs, goes to the 

 posterior seta, and the articulated appendage ; the middle furnishes 

 the basal joint, and sends a branch into the terminal ; the outer 

 affords a small nerve to the seta at the apex of the basal joint, and 

 then passes into the extreinity of the leg. 



This pair of nerves give off a branch exteriorly near their ori- 

 gin, (s, fig. 20, ) which curves outM'-ard under the furcate process, 

 (s, fig. 18,) beneath the ventral muscles, gives a nerve to these 

 muscles, and is then distributed to the anterior muscles of the 

 second pair of natatories, and to the adjoining teguments. Its 

 branches may be seen at s^, s'', fig. 18. 



The spinal cord, furnishes the nerves to the remaining mem- 

 bers. It appears to be composed of two parts near its cmgin, but 

 there is no division till it has passed beyond the sternum of the 

 second pair of natatories. Previous to this division, a short dis- 

 tance below the sternum, this spinal cord gives off from each side 

 a large nerve which goes to the apron. These nerves are seldom 

 exactly opposite in their origin j as is also the case with the nerves, 

 r and s, fig. 20. 



The nerves to the apron, just before entering it, give off a branch 

 exteriorly, which is distributed to the outer portions of the apron, 

 or more properly its terminal joints. Soon after entering the 

 apron the main nerve again divides, and one branch is distributed 

 to the basal part, and the other to the muscles of the following 

 portion of the apron. 



The spinal cord, after giving off the nerves to the apron, soon 

 divides. Thus divided, it gives off a pair of nerves to the re- 

 maining thoracic legs, and on entering the abdomen, furnishes a 

 pair of nerves which branch in this segment. It thence con- 

 tinues to the last segment, and distributes fibres to the terminal 

 portions of the body. 



