§ 298. THE ARACHNOIDAE. 3869 
moulting, is a layer of colored vesicles and granules, which can be seer 
through the skin, giving it the often very beautiful colors which are 
observed in many species. 
The various divisions of the cutaneous skeleton, of which the number is 
quite limited, have been so thoroughly studied in zoology, that they may 
well be passed over here without notice. 
The Cephalothorax sends off from its inner surface, especially with the 
Opilionina, and Araneae, various processes, which serve, as with the Crus- 
tacea, as points for the insertion of muscles, and as septa between certain 
organs. With the Araneae, they form, at the bottom of the cephalothorax, 
a solid horizontal plate, —a kind of internal skeleton, which, before and 
behind, is attached to the sternum by two tendinous ligaments. This plate 
is deeply indentated on its anterior border, and furnishes points of inser- 
tion for the muscles of the extremities, as well as for several other 
parts.“ 
CHAPTER II, 
MUSCULAR SYSTEM AND ORGANS OF LOCOMOTION. 
§ 298. 
The voluntary muscles of the Arachnoidae are of a dirty-yellow color, 
and, like those of the Crustacea, are distinctly striated transversely.” Their 
general disposition agrees, also, with those of Crustacea.” 
The principal muscular masses are found in the cephalothorax, for here 
arise, not only the muscles of the parts of the mouth, but also those of the 
first article of the tactile organs and legs. With those species having an 
unarticulated abdomen, the muscles of this part of the body differ from 
. those of Crustacea. For, directly beneath the skin, is a thin layer, com- 
posed of numerous short, riband-like fibres, interlaced in various directions, 
and frequently anastomosing with each other. Moreover, with many spe- 
cies, there are, on both the dorsal and the ventral surface of the abdomen, 
depressions of the skin, from which pass off small muscular bands, which 
penetrate into the interior of the abdomen, and pass among the viscera. 
With the Araneae there is, generally, on each side of the ventral median 
4 This plate, already recognized by Lyonet (loc. 
cit. p. 405, Pl. XXI. fig. 26), and by Treviranus 
(Bau d. Arach. Taf. IT. fig. 23), has been described 
more exactly by Wasmann (loc. cit. p. 2, fig. 
2-4). A similar, but rudimentary plate, exists, 
perhaps, with Phalangium, and, as it lies under 
the ventral cord, the muscles have the appearance 
of rising from this last ; see Tw/k, loc. cit. p. 325, 
or in Froriep’s neue Notiz. XXX. p. 186. 
1 The Tardigrada form an exception in this re- 
spect, their muscles being smooth; see Doyére, 
loc. cit. p. 336. 
2 For the disp and arr 
system of Scorpionid 
t of the 
and Araneae, see 
Meckel, Syst. d. vergleich. Anat. IIT. p. 47; and 
for the muscles of Phalangium and Mygale, see 
Tulk, and Wasmann, loc. cit. The very compli- 
cated muscular system of the Tardigrada is quite 
apparent from the transparency of these animals ; 
see Doyere, loc. cit. p. 338, Pl. XVII.-XIX. 
3 This cutaneous layer, already observed by 
Treviranus (Verm. Schrift. I. p. 9, Taf. I. fig. 3, 
a.n.), and by Brandt (Mediz. Zool. I. p. 88, Taf. 
XV. fig. 8, a. a., or Ann. d. Sc. Nat. XIII. p. 180, 
Pl. IV. fig. 1, a. a.), with Epeira, has been con- 
firmed by Tuk (loc. cit. p. 154) with Phalan- 
gium, and described in more detail by W’asmann. 
(loc. cit. p. 8, fig. 7, 8) with Mygale. 
