318 THE CRUSTACEA. § 272. 
together laterally, on the median line. Of these, the first six pairs, belong- 
ing to the thoracic and to the anterior abdominal segments, are the larger, 
and send off nerves principally to the foot-jaws, to the prehensile, and to the 
ambulatory organs. The two longitudinal commissures between the anterior 
abdominal ganglia, are separate; but those between the posterior ganglia are, 
on the contrary, blended into a single cord. In some species, these com- 
missures are wholly wanting between the anterior ganglia.© The brain 
consists of a single transverse ganglion; from its front and sides pass off 
several nerves for the antennae, the olfactory organs, the eyes, and the 
auditory organs; while, from behind, it sends off the two long cords which 
surround the cesophagus. These last give branches on their course to the 
organs of mastication, and interanastomose behind the oesophagus, just 
before reaching the first thoracic ganglion, by a transverse filament.” 
__ With the Stomapoda, the nervous system is composed of a cerebral gan- 
glion, and of about ten abdominal ganglia; of these, with the Squillina, the 
last six belong to the tail, while the remaining four, anterior, send nerves to 
the thorax, and to the first three abdominal segments, The size of the first, 
which sends nerves to thé prehensile feet, is due to its being composed 
of several ganglia fused together.” With the Mysina, the five or six 
largest ganglia belong to the thorax and to the anterior part of the abdo- 
men, and are connected together by short, double commissures.® 
The genus Phyllosoma has two extraordinarily long and very small 
«esophageal cords extending from the brain to the abdominal cord. The 
thoracic portion of this last is composed of three pairs of ganglia, blended 
almost into a single mass; these are succeeded by six pairs of large ab- 
dominal ganglia, arranged in two longitudinal rows, and interconnected by 
six very short, transverse filaments. In the short tail, there are, more- 
over, six pairs of ganglia, smaller and laterally contiguous, but connected 
successively by very small longitudinal filaments. ; 
With the Anomoura, which resemble the Brachyura in the abortion of 
the post-abdomen, the structure of the nervous system confirms this affi:. 
ity. With Pagurus, the anterior portion of the abdominal cord consists 
only of three ganglia, which send nerves to the foot-jaws, to the cheliform, 
and to the partially abortive ambulatory feet. But the posterior part of 
this cord consists of two cords which arise from the third abdominal gan- 
glion, and unite, just in front of the arms, in the fourth and last gan- 
glion.© With the genus Homola, the five pairs of the anterior abdomi- 
nal ganglia are fused into a single mass which is perforated through its 
centre. From the posterior border of this mass a simple nervous cord 
as rudiment of the posterior part of the ventral cord, passes off to the wholly 
abortive post-abdomen.® 
With the Brachyura, the nervous system has only two central masses, 
one cerebral, the other abdominal. The first sends nerves, as in the other 
8 Palinurus, and Palaemon (dudoutn and 
Milne Edwards, loc. cit.). In these two Crusta- 
cea, there is only a small fissure in the centre of 
the principal ganglionic mass, after the fusion of 
5 Cuvier, Legons &c. III. 1845, p. 330, and 
Delle Chiaje, Descriz. &c. Tay. LXXXVI. fig. 
5 
6 Frey, De Mysidis flexuosae anat. p. 9. 
the ganglia. 
4 This transverse filament is absent neither with 
Palaemon, Palinurus, nor with Homarus, and 
Astacus. It was overlooked by Suckow in the 
crawfish, although distinctly seen by Brandt ; see 
his Medizin. Zool. loc. cit., and his Bemerkungen 
aber die Mundmagen-nerven, loc. cit. Tab. I. fig. 
1,2E., or Ann. d. Sc. Nat. V. 1836, Pl. IV. 
7 Audouin and Milne Edwards, Ann. d. Sc. 
Nat. loc. cit. p. 81, Pl. III. : 
8 Cuvier, Legons, &c., loc. cit. p. 329; and 
Owen, Lect. on Comp. Anat. p. 170. 
“ 9 Milme Edwards, Hist. Nat. d. Crust. Pl. XI. 
g. 9. 
