NERVOUS SYSTEM. 91 



Just in front, at the outside corners of the two supra- 

 cesophageal ganglions (b), a branch (ef) arises, which I 

 traced to the ends of the adductor scutorum muscle, and to 

 those several muscles which serve to retract the interspace 

 of membrane between the mouth and the adductor. 



The pair of great splanchnic nerves above alluded to, 

 which arise from the anterior and dorsal surface of the 

 infra- oesophageal ganglion, are in PL 27, fig. 1, d d, (and 

 in fig. 2), laid flat ; but in nature they first bow outwards, and 

 then, penetrating deeper into the body, approach each other, 

 and running nearly parallel, pass round the lower end of 

 the oesophagus : their course consequently is nearly similar 

 to that of the circa-cesophageal chord, with this difference, 

 that the outwardly bowed portion is situated near the infra- 

 cesophageal, instead of near the supra-cesophageal ganglion. 

 The splanchnic nerve, a little beyond the supra-cesophageal 

 ganglion, joins a plexus (d') ; and into this plexus another 

 large nerve (e) which T will call the supra-splanchnic nerve, 

 sends branches ; this nerve takes an almost semicircular 

 bend over the ovarian glands. The supra-splanchnic nerves 

 (e, e), though appearing to spring from the supra-cesophageal 

 ganglions, do really arise, as may be seen by tracing the con- 

 stituent fibres, from the circa-cesophageal chord. The plexus 

 (d' ) lies close to the coats of the upper end of the stomach : 

 several branches, proceeding from it, run further on, but I 

 was able to trace only a few of them : one went (at least in 

 the case of Balanus perforatus), to the adductor scutorum 

 muscle : another branch spread out on the flanks of the 

 prosoma : I strongly suspect that one branch goes to the 

 acoustic sack : it appeared, also, as if some of the small 

 branches entered the second plexus (m), where the inner 

 antennular nerve and ophthalmic nerve cross over the outer 

 antennular nerve. 



I have called the nerves (dd, ee) splanchnic and supra- 

 splanchnic, from their course and apparent function in 

 supplying the viscera. In the descriptions of the nervous 

 system of other Crustaceans I can find nothing analogous 

 to my great splanchnic nerve (dd) ; the so-called supra- 

 splanchnic nerves (ee), which arise from the circa-cesophageal 

 chord, seem to be the analogues of the ordinary splanchnic 



