322 THE CRUSTACEA. "§> 273. 



lestium, the cerebral ganglion is entirely wanting, but, in its stead, there is 

 a conspicuous thoracic ganglion under the oesophagus, from which passes off 

 an equal number of nerves in front and behind, and which is succeeded, 

 posteriorly, by a large nervous trunk as the abdominal cord. This cord 

 has ganglionic enlargements in the three anterior abdominal segments, and 

 finally divides into two branches which extend to the very extremity of the 

 tail.*"' With Achiheres, and Peniculus, the nervous centres consist only 

 of two trunks lying on the lower surface of the abdomen, each side of the 

 intestinal canal.*''-' 



With the Cirripedia, which are headless, the nervous centre consists of 

 two parallel abdominal trunks, which, in their course, form six to seven 

 ganglionic enlargements from which pass off, laterally, nerves to the cirri. 

 The two anterior ganglia are connected by a nerve which stretches arcu- 

 ately over the oesophagus, and sends filaments to the organs of mastication, 

 so that a brain proper is wanting. The last two pairs of ganglia are 

 blended into a single mass, which sends nerves to the cirri, and two fila- 

 mens into the long tail.*'"* 



§273. 



The Vegetative nervous system is distinctly developed with many Crus- 

 tacea. It consists of a single or of a double Splanchnic nerve. 



With the Decapoda, and Squillina, a single splanchnic nerve arises from 

 the posterior border of the brain, — passes over the stomach, at the same 

 time enlarging into one or two ganglia, distributes its branches to the walls 

 of this organ, and, finally, enters the liver right and left. 



This nerve is reinforced by two filaments, which, conjointly with the 

 nerves of the masticatory organs, are given off from the ganglionic enlarge- 

 ments of the two oesophageal commissures, and, before entering the 

 splanchnic nerve, send off filaments directly to the lateral walls of the 

 stomach. *^' 



With the Oniscidae, there are two splanchnic nerves. On each side of 

 the small stomach are two ganglia which connect with the brain by a short 

 filament, and send off, posteriorly, small branches to the walls of the stom- 

 ach. *2' 



With the Myriapoda, there are also two systems of splanchnic nerves. 



31 Rathki, njid. XIX. p. 150, Tab. XVII. fig. Krohn, Isia, 1834, p. 529, Taf. Xn. fig. 1-4, and 

 3, 4. Schlemm, De hepate ac bile Crustaceorum et Mol- 



32 Nordmann, Microgi-. Beitr., Hft. 2, p. 72, 109, luscorum, loc. cit. p. 16, Tab. I. fig. 2, Tab. II. fig. 13 

 Taf. V. fig. 7, J., 6. (Jstacusjluviatilis). Suckoxo (loc. cit. p. 62, Tab. 



33 Cuvier, Mem. loc. cit. p. 11, fig. 11, and XI. fig. 7, g.) in the Crawfish, and iVei/);)or( (Philos. 

 Martin St. An^e, loc. cit. p. 18, PI. II. fig. 8 Trans. 1834, PI. XVII. fig. 40, f.)m the lobster, have 

 (^Lepas) ; also IVyman in SiUiTnan^s Amer. Jour, observed only a single splanchnic nerve, which they 

 XXXIX. 1840, p. 182 {Otion).* have regarded as a cardiac nerve. Audouin and 



1 We are indebted to Brandt for very complete jV/r/ne -Ef/ifards, on the other hand, have described 



contributions on the sympathetic system of the and figured with botli the Macrura and the Bra- 



Decapoda ; see his Bemerk. iiber d. Mundmagen- chyura, double splanchnic nerves, but the single 



Oder Eingeweidenerven der Evertebr. loc. cit. p. 7, one was entirely overlooked. 



Tab. I. fig. 1-3 I^Astacus and Squilla)., (also in the 2 Brandt, Bemerk. &c. p. 14, and Medizin. Zool. 



Ann. d. Sc. Nat. V. 1836, p. 87, PI. IV. and in the II. p. 75, Taf. XV. fig. 27, c. 

 Mediz. Zool. U. Taf. XI. fig. 1, i.) ; see, also, 



* [ ^ 272, note 33.] Subsequent researches have class Cirripedia, &c., p. 48 (Lepas). Even in the 



shown that with some at least of the Cirripedia, description referred to above, of Otion, by Wyman 



there is a proper brain furnishing nerves to the in SiUiman^s Jour., a brain ia really spoken of. — 



organs of seuse ; see Darwin, Monogr. of the sub- En. 



