374 THE ARACHNOIDAE. «§>^ 303, 304, 305. 



CHAPTER IV. 



ORGANS OF SENSE. 



§ 303. 



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-articulated 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. ''' 



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. Each of these eyes is enveloped, before 

 and behind, by a pigment tunic corresponding to the Chorioidea ; its color 



I See § 806. Latreille (R^gne auim. IV. 1829, Obisium, Chelifer, Phrynus, and Thelyphonus, 



p. 207), has regarded these mandibles as trans- the palpi are forficulate, and are used as prehensile 



formed antennae, but usually they have been con- organs. 



sidered as the first pair of maxillae. This view 3 See Treviranus, Zeitsch. f. Phys. IV. p. 94, 



of Latreille is the correct one, since the nerves of Taf. VI. fig. 4, No. 4 (a Brazilian spider), and 



those organs do not arise from the abdominal Doijire, loc. cit. p. 349, PI. XVII. fig. 1, n. a. 



ganglia, but directly from the brain, as those of (_Milnesium). 



the antennae of Crustacea and Insecta. 1 .According to analogy, the sense of taste, with 



n These palpi are wanting with Pycnogonum, the Arachnoidae, is seated probably at the entrance 



Phoxichilus, Phoxichilidium and Pallene ; see of the oesophagus. 



Savigny, Mem. loc. cit. I. PI. V. fig. 3 ; Johns 1 The eyes are wanting with Demodex, Sar- 



ion, Ma'/, of Zool. and Bot. I. PI. XI [I. fig. 1-8 ; copies, Pteroptu-i, Dermanyssus, Gamasus, 



Milne Edwards, Hist. Nat. d. Crust. PI. XLI. Thyroglyphus, Glycyp/iagus, Acarus, Argas, 



fig. 6. With the Scorpionidae, as well as with Ixodes, <Si.c. 



