82 THE ECHINODERMATA. $$ 79, 80. 
CHAPTER III. 
NERVOUS SYSTEM. 
§ 79. 
The central portion of the nervous system consists of a ring which is 
usually pentagonal, and surrounds the commencement of the csophagus. 
The main nervous branches are given off from this, and pass to the other 
end of the body along the median line of ‘the rays, or their corresponding 
parts. The form of this ring is mainly due to that of the mouth; and 
therefore, with the reniform mouth of Spatangus, it is unequally pentago- 
nal.. Ganglia have not yet been found in it. But in Echinus and Holo- 
thuria, the nerves passing from it have between their fibres, violet, green, 
or red pigment granules. 
§ 80. 
The principal nervous trunks have a longitudinal furrow, as if composed 
of double cords, and give off from each side, during their course, branches 
which go to the ambulacra.” : 
With the Crinoidea, a nervous cord passes beneath the furrow formed 
by the perisoma on the ventral surface of the arms; this has a slight 
swelling opposite each pinnula, to which it sends off a branch. With 
the Asteroidae, the nervous trunks which pass off from the cesophageal ring 
are lodged in the ventral furrows of the rays. But in the Ophiuridae, 
they pass in a canal, concealed by the ventral plates of the arms. The 
five nerves, analogous to those of the Hchinoidea, pass along the internal 
surface of the ambulacral plates, between the vesicles, even to the centre 
of the dorsal region. In Echinws, there are, moreover, special nerves 
directly from the cesophageal ring, for the organs of mastication and 
digestive canal. In Holothuria, this ring is situated directly on the 
anterior border of the osseous circle, and sends off five nerves which pass 
along the median line of the longitudinal muscles, even to the end of the 
body ;® it sends off also special nerves to the oral tentacles. 
1 Krohn (Miiller’s Arch 1841, p. 8, Taf. I. fig. 
3,4 
, 4). 
2 Krohn, loc. cit. 
1 Krohn, ibid. p. 4, 10. 
2 Muller (Abhandl. d. Berl. Akad. loc. cit. p. 
233, Taf. IV. fig. 11, i.; Taf. V. fig. 16). 
3 The nervous system of the Asteroidae was first 
clearly shown by Tiedemann (loc. cit. p. 62, 
‘Taf. IX. and Meckel’s Deutsch. Archiv. I. 1815, 
p. 69, Taf. Il. fig. 1). This anatomist, like 
Krohn (loc. cit. p. 4), did not perceive the ganglia 
of the cesophageal ring, observed by Wagner 
(Vergleich. Anat. 1834, p. 372). 
The ganglia and nerves that Spi (Ann. du 
Mus. d’Hist. Nat. XIII. 1809, p. 439, Pl. XXXII. 
fig. 3, 6) and Konrad (De Asteriarum fabrica 
dissert. 1814, p. 13, fig. 3, 0.) affirm to have seen 
on the internal (dorsal) surface, opposite the ventral 
*(§ 80, note 6.] Muller has furnished some 
valuable contributions on the nervous system of the 
furrows of the articulations of the rays, in Aster- 
acanthion rubens, and glacialis, are probably 
only tendinous fibres. 
4 Krohn, who has studied the nervous system 
of Echinus and Spatangus, has traced the fila- 
ments given off from the main trunks, across the 
ambulacral pores, to the suckers of the ambulacra. 
See also Valentin’s figures of this system, in 
Echinus (Monogr. loc. cit. p. 98, Pl. VILL. LX.). 
5 The cesophageal ring of Ho/othuria, observed 
by Krohn (Miller’s Arch. 1841, p. 9, Taf. I. fig. 
5), sends off its principal nerves across the fissures 
of the dentations of the five great pieces of the 
osseous rings. Their lateral filaments, going to the 
ambulacral vesicles, are so fine that Krohn could 
scarcely find them. 
6 Grant, loc. cit. p. 184.* 
Holothurioidea ; see Arch. 1850, p. 226. We 
makes this statement, which is worthy of remem- 
