A Monograph on the Sub-class Cirripedia · Charles Darwin
NERVOUS SYSTEM AND SENSES.
Fig. 1, Nervous system of _Coronula diadema_, seen from the ventral surface. A, infra-œsophageal ganglion; two pairs of rather small nerves, arising from the dorsal surface, cannot be here shown. B, supra-œsophageal ganglion, double. C, ophthalmic ganglion, single. D D, eyes, as believed to exist. _a_, three pairs of nerves, running to the gnathites and olfactory pouches; _a′_, nerve rising from the collar, running towards the mandibles. _b_, single medial nerve, running to the great transverse muscle, extending across the upper part of the stomach. _c_, collar-nerve or chord, uniting the infra- and supra-œsophageal ganglions. _d_, great splanchnic nerve, here spread laterally out, but properly running along the sides of the upper part of the prosoma, and therefore under the collar-nerve; _d′_, plexus by which this nerve is connected with the supra-splanchnic nerve, _e_. _e_, supra-splanchnic nerve, rising from the collar, almost in contact with the supra-œsophageal ganglion; _e′_, small nerve rising from the end of the supra-œsophageal ganglion, and running to the adductor and surrounding muscles. _f_, _f_, pair of great nerves (_antennular_), distributed over the sack and shell. _g_, chord (in appearance single), uniting the supra-œsophageal ganglion with the first (C), or ophthalmic ganglion. _h_, small medial nerve, running to near the adductor muscle. _i_, nerve supposed to run from the ophthalmic ganglion to the eye. _k_, small nerve, rising from the main ganglion (A), between _r^1_ and _r^2_, or the nerves running to the first and second pairs of cirri. _œ_, position of the œsophagus. _r^1_ nerve entering the first cirrus. _r^2_, _r^3_, _r^4_, _r^5_, _r^6_, nerves entering the five succeeding pairs of cirri. _s_, nerve entering the probosciformed penis. 2, nervous system of _Balanus tintinnabulum_; letters of reference as in fig. 1. 3, acoustic sack of _Balanus tintinnabulum_. 4, " " _Coronula diadema_. 5, eye of _Balanus tintinnabulum_; _i_, nerve coming from the ophthalmic ganglion; D, eye itself.
Text from Project Gutenberg, public domain in the United States.