1336 



CRUSTACEA. 



backward, and is supposed to furnish nerves to the posterior 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 extremity of the leg. 

 This pair of nerves give off a branch exteriorly near their origin (s, 

 iig. s) which curves outward under the furcate process (s, fig. 1 q), 

 beneath the ventral muscles, sends a nerve to these muscles, and is 

 then distributed to the anterior muscles of the second pair of nata- 

 tories, and to the adjoining teguments. Its branches may be seen at 



The central cord furnishes the nerves to the remaining members. 

 It appears to be composed of two parts near its origin, but there is no 

 division till it has passed beyond the sternum of the second pair of 

 natatories. Previous to this division, a short distance below the 

 sternum, this cord gives off from each side a large nerve which goes 

 to the apron. These nerves are seldom exactly opposite in their 

 origin; as is also the case with the nerves, r, r, and s, r, fig. s. 



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 central cord, after giving off the nerves to the apron, soon 

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

 thoracic legs, and on entering the abdomen, furnishes a pair of nerves 

 which branch in this segment. It thence continues to the last seg- 

 ment, and distributes fibres to the terminal portions of the body. 



The nervous system in Caligus agrees with that of Sapphinna in 

 the existence of but a single compound ganglion for the whole body, 

 there being no separate ganglia for the posterior thoracic or abdominal 

 segments and their members. But the two differ strikingly in form, 

 as shown in the figures (2 g, Plate 88, and 1 s, Plate 93). In Sap- 

 phirina, the large ganglion is furcate behind, and the two stout pro- 

 longations, after passing a short distance, give off, each four nerves, 



