320 THE CRUSTACEA. § 272. 
distinct right and left half, upon each of which is a kind of Ganglion 
opticum, of a size proportionate to that of the development of the eyes. 
With the Chilopoda, the abdominal ganglia are widely separated from 
each other, but connected by double commissures which are closely ap- 
proximated, and in some cases, fused together as a ventral cord.°? With 
Lithobius, and Scutigera, there are sixteen pairs of these ganglia; with 
Scolopendra, twenty-two, and with Geophilws, fifty to one hundred and 
forty. Of these ganglia, the first pair, belonging to the two anterior feet,. 
which are changed into prehensile or tactile organs, are much the largest. 
The size of the others corresponds, for the most part, to the development 
of the feet. 
Of the Chilognatha, the genus Polydesmus, the long feet of which are: 
widely separated, is. allied to the preceding section of Myriapoda. Above: 
each two pairs of feet, the abdominal cord is enlarged into two successive 
ganglia, and the medullary mass between them corresponds to a simple 
longitudinal commissure. With the other Chilognatha, of which the 
pairs of feet are close together, the longitudinal commissures are wholly 
wanting, so that the ganglia, of a number corresponding to that of the 
pairs of feet, form a moniliform cord; and in some Julidae, the constric- 
tions of this last are entirely effaced. P 
The disposition of the nervous system of Lémulus is remarkable. Its 
principal mass surrounds the mouth like a ring. From the anterior por- 
tion of this, corresponding to a brain, pass off nerves in front, among which 
the two optic nerves are conspicuous for their length ; while its posterior 
are, which surrounds the cesophagus, has three transverse commissures suc- 
ceeding each other. From the lateral portions of this ring, pass off six 
pairs of large nerves for as many pairs of prehensile feet.. From its pos- 
.terior border arises a large trunk composed of two bands which extend 
- backwards along the median line of the abdomen, furnishing nerves to the 
fin-like and gill-like appendages, and then separating, terminate in the tail 
in a ganglion from which are given off many filaments to the neighboring 
parts, and a very long one which enters the caudal spine. 
Of the nervous system of the Phyllopoda, that of the genus Apus is the 
best known.” The brain consists of a flattened, quadrilateral body, from 
the superior angles of which arise the optic nerves, while from the posterior 
angles pass off the two long, oesophageal commissures. These last, before 
-reaching the thoracic ganglia, are connected by a transverse commissure. 
Upon the thoracic succeed numerous abdominal ganglia, those of each pair 
of which, as in the first, are wide apart, but they gradually. approximate 
posteriorly, and at last are fused into a single mass. ‘ 
The two thoracic ganglia, as well also as the anterior abdominal pairs, 
21 Geophilus. 
22 Treviranus, Verm. Schrift. II. p. 31, Taf. 
VIL. fig. 2, 5 (Lithobius and Geophilus); Ku- 
Verm. Schrift. II. p. 16, Taf. IX., and Newport, 
Phil. Trans. 1843, p, 247, Pl. XI. fig. 1. The 
number of ganglia increases in general with the 
torga, loc. oit. p. 15, Tab. II. fig. 2, Tab. III. fig. 
1, 2 (Scolopendra morsitans); but especially 
Newport, Philos, Trans. 1834, p. 408, Pl. XVII. 
fig. 43-48 (Scolopendra), and 1843, p. 257, Pl. XI. 
fig. 11-13 (Geophilus). : 
23 Newport, loc. cit. 1843, p. 252, Pl. XI. fig. 
6, 10, or Owen, Lect. &c. p. 200, fig. 99. 
24 There are only six pairs of ganglia with 
Glomeris ; see Brandt, in Muller’s Arch. 1837, 
p. 324, Taf. XIT, fig. 6. But these ganglia are 
‘very numerous with Julus; see Treviranus, 
increase of the body together with that of the num- 
ber of the segments and feet. 
2 Van der Hoeven, Recherch. &c. p. 21, PL 
IIL. fig. 2, 3. 
26 This system has been described by Gaede 
Wiedemann’s Zool. Magaz. I. Stiick 1, p. 91, Tag. 
- fig. 1), and by Berthold (Isis, 1830, p. 690, Taf. 
VII. fig. 4). But for the most careful researches: 
on this subject we are indebted to Zaddach (loc. cit. 
p. 35, Tab, IIL.) 
