8T4 THE ARACHNOIDAX. ¥$ 808, 804, 305. 
CHAPTER IV. 
ORGANS OF SENSE. 
§ 308. 
The multi-articulated antennae with which the Crustacea and Insecta are 
endowed, are absent with the Arachnoidae, or, more properly speaking, they 
are changed into prehensile and masticatory organs.” 
The palpi, which are absent with only a few Arachnoidae,® must be re- 
garded as the principal seat of the sense of Touch. These tactile organs 
always receive two considerable nerves arising from the anterior extremity 
of the ventral ganglionic mass. A very delicate sense of touch exists, 
also, in the extremity of the feet, which are well supplied with nerves; 
and, for this object, the feet of the Opilionina and Phrynidae have the 
form of multi-artieulated antennae. 
With the Araneae, this point admits of no doubt, for these organs (the 
feet) are especially used in the formation of the web. 
§ 304. 
Although we must grant to the Arachnoidae the sense of Taste, and that. 
of Smell; and although many facts show that they have the sense of Hear- 
ing highly developed, yet, at present, nothing satisfactory has been discov- 
ered either as to the locality or the structure of the organs which are the 
seat of these senses.” 
§ 305. 
The organs of Vision of the Arachnoidae consist always of simple eyes 
(Stemmata); but among the lower Arachnoidae, there is a complete series, 
namely, the parasitic Mites, and allied groups, which are entirely deficient 
in these organs. ae 
The stemmata of the Arachnoidae have exactly the same organization as 
the simple eyes of the Crustacea. They are composed of a simple and 
convex cornea, of a spherical lens, and of a concavo-convex, vitreous body, 
which is surrounded by a Retina. Hach of these eyes is enveloped, before 
and behind, by a pigment tunic corresponding to the Chorioidea; its color 
1 See § 306. Latreille (Régne anim. IV. 1829 
p. 207), has regarded these mandibles as trans- 
formed antennae, but usually they have been con- 
sidered as the first pair of maxillae. This view 
of Latreiile is the correct one, since the nerves of 
those organs do not arise from the abdominal 
ganglia, but directly from the brain, as those of 
the antennae of Crustacea and Insecta. 
2 These palpi are wanting with Pycnogonum, 
Phozichilus, Phoxichilidium and Pallene ; see 
Savigny, Mém. loc. cit. I. Pl. V. fig. 3 ; Johns 
ton, Mag. of Zool. and Bot. I. Pl. XIII. fig. 1-8 5 
Miine Edwards, Hist. Nat.d. Crust. Pl. XLI. 
fig. 6. With the Scorpionidae, as well as with 
Obisium, Chelifer, Phrynus, and Thelyphonus, 
the palpi are forficulate, and are used as prehensile 
organs. 
8 See Treviranus, Zeitsch. f. Phys. IV. p. 94, 
Taf. VI. fig. 4, No. 4 (a Brazilian spider), and 
Doyere, loc. cit. p. 349, Pl. XVIL. fig. 1, n. a. 
(Miinesium). 
1 According to analogy, the sense of taste, with 
the Arachnoidae, is seated probably at the entrance 
of the cesophagus. 
1 The eyes are wanting with Demoder, Sar- 
coptes, Pteroptus, Dermanyssus, Gamasus, 
Thyroglyphus, Glycyphagus, Acarus, Argas, 
Tzodes &c. 
