$$ 300, 301. TUE ARACHNOIDAE. 371 
CHAPTER III. 
NERVOUS SYSTEM. 
§ 300. 
The grades of development of the Nervous System with the Arachnoidae 
are very different, being connected with the divisions of the cutaneous skel- 
eton. For, when these last disappear, those of the nervous system belong- 
ing to them, and often the ventral cord, are concentrated, as with the 
brachyurous Decapoda, into a single ganglionic mass, occupying the ventral 
portion of the cephalothorax ; while, if the body is multi-articulate, this sys- 
tem resembles that of the macrurous Decapoda. In both cases, with only 
a few exceptions, there is a cerebral ganglion situated above the esophagus, 
and connected with the ventral cord by two short commissures surrounding 
this canal. From this ganglion pass off nerves to the eyes, and the maxil- 
lary palpi or so-called mandibles; while the first pair of maxillae, changed 
into tactile organs, receive their nerves from the anterior extremity of the 
ventral cord. 
The intimate structure of the nervous system, with the Arachnoidae, con- 
sists of primitive fibres much finer, and ganglionic globules much smaller, 
than those of Crustacea. As to the direction and disposition of these 
fibres, those of the Scorpionidae almost exactly resemble those of the 
Myriapoda. 
§ 301. 
The nervous system is most simple in its organization with the Acarina. 
In those species where, as yet, it has been found,” it consists only of a 
simple abdominal ganglion, from which pass off, from all sides, the peri- 
pheric nerves; and, upon the upper surface of which, is detached a simple 
transverse band, under which the osophagus passes. 
With the Tardigrada, this system isa little more developed, although 
the brain is still wanting.” It consists of four ganglia, corresponding to 
the four segments of the body, and connected together by double longitudi- 
nal commissures. Between each of the ganglia, the commissures are con- 
nected by a transverse filament. The nerves which proceed from the 
ganglia belong to the muscles; but the first ganglion sends, moreover, in 
front, four larger trunks, which are the nerves of sense, and are distributed 
to the eyes and palpi.® 
1 Hannover, loc. cit. p. 71, Pl. VI. fig. 83, 84. 
2 See § 271, and Newport, Philos. Trans. 1843, 
loc. cit. 
1 With many small Acarina, particularly Sar- 
coptes and Demodez, no traces of a nervous sys- 
tem have been found, notwithstanding the most 
careful researches ; but this is not surprising, con- 
sidering the minuteness of these animals. 
2 Treviranus (Verm. Schrift. I. p. 47, fig. 82) 
has investigated the nervous system of Trom- 
didium, and the results he obtained have been 
confirmed with this genus and with Lemnochares, 
by Dujardin (Ann. d. 8c. Nat. III. p. 19). Sub- 
sequently, Treviranus (Zeitsch. f. Physiol. loc. 
cit. p. 189, Taf. XVI. fig. 7. c.) has also con- 
firmed, with Ivodes, this passage of the esophagus 
through the principal ganglionic mass. With 
Trombidium, whose ganglion is somewhat reddish, 
the cerebral i e is quite disti 
3 See Doyere, loc. ct. p. 343, Pl. XVII. (Milne- 
sium). 
