388 THE ARACHNOIDAE. § 815. 
II. Organs of Special Secretions. 
§ 316. 
Very many Arachnoidae have Poison-glands, the product of which is 
excreted through the extremity of a hollow claw. With the Phrynidae, the 
Araneae, and some Acarina, there are two such glands in communication 
with the terminal hooks of the cheliceres. They have been often taken for 
salivary organs. With the Trombidina, there are, on each side of the 
cephalothorax, two small, flexuous, colorless, glandular tubes, which, at 
their anterior extremity, are dilated, each, into a cylindrical, thin-walled 
poison-reservoir. From this reservoir arises a long, narrow canal, which 
runs to the cheliceres.” With the Araneae, the poison-apparatus consists 
of two tubes, often a little curved, and surrounded by a layer of flattened, 
spiral, muscular fasciculi.” These two glands are situated at the base of the 
cheliceres, extend more or Jess into the cephalothorax,® and, in front, be- 
come suddenly attenuated, forming a narrow excretory duct which termi- 
nates at the apex of the hollow claw of the cheliceres.® With the Scor- 
pionidae, this apparatus is situated in the last caudal segment; it consists 
of two oval vesicles, whose excretory ducts open at the apex of the sting 
situated on the end of the tail. ‘These two glands are surrounded by a 
layer of flat, circular, smooth, muscular fasciculi.© 
With the Araneae, there is another and very remarkable secretory appa- 
ratus, — the Silk organs. Its product is a viscous, transparent liquid which 
hardens quickly on exposure to the air, forming threads. It escapes by 
three, rarely by two pairs of spinnerets, situated behind the anus.© The 
glands which secrete it are composed of transparent nucleolated cells, and 
are of very variable form and disposition, but always situated in the midst 
of the abdominal viscera. About five kinds of these glands may be dis- 
tinguished, although not always simultaneously in the same individual. 
The threads have probably different qualities, according to the glands from 
which they are secreted. 
The genus Epeira, containing all these five kinds of glands, will serve as 
the type for their description. There are observed: 1. Small pyriform 
follicies, aggregated in groups of hundreds, and having short excretory 
1 The two poison-glands of the Trombidium ho- 
losericeum, and Rhyncholophus phalangiotdes, 
have the form of a ring with a small opening. 
Treviranus (Verm. Schrift. I. p. 48, Taf. VI. fig. 
34) has described only very imperfectly these 
glands with the first mentioned of these animals ; 
and not having seen their excretory ducts, he took 
them for salivary glands. Dugeés (Ann. d. Sc. 
Nat. II. p. 10), on the contrary, perceived their 
true relation to the cheliceres. 
2 It is remarkable that these muscular fasciculi 
present such different histological characters. I 
have seen them distinctly striated with Lycosa, 
Drassus, Tegenaria and Micryphantes. They 
are smooth with Epeira, Thomisus, Clubiona 
and Mygale ; with Salticus, they present obscure 
transverse lines, so that Iam undecided whether 
they belong to the first or to the second of these 
categories. 
3 With Mygale, these glands are entirely con- 
cealed in the basilar article of the cheliceres. 
4 Treviranus, Bau d. Arachn. p. 31, Taf. II. 
fig. 21, 22; Lyonet, loc. cit. p. 397, Pl. XX. fig. 
16,175 Brandt, Mediz. Zool. Il. Taf. XV. fig. 6, 
or Ann. d. Sc. Nat. XIII. Pl. IV. fig. 2; and 
Wasmann, loc. cit. p. 19, fig. 25, 26. For the in- 
timate structure of these glands, see Meckel, in 
Miiller’s Arch. 1846, p. 35. 
5 Miller, in Mecked’s Arch. loc. cit. p. 52, Taf. 
I. fig. 7,8. Serres (loc. cit. p. 90) regards the 
portion of these glands which is surrounded by 
muscular fibres, as a reservoir of poison, and that 
this last is secreted by innumerable glandular folli- 
cles enveloping the muscular layer. In fact, with 
Scorpio europaeus, I have seen this layer covered, 
externally, with a stratum of cylindrical cells. 
6 The Mygalidae have two pairs of these papillae, 
or spinnerets, instead of six, the usual number. 
7 I speak here upon the careful investigations of 
Hl. Meckel (Miiller’s Arch. 1846, p. 50, Taf. IIL 
fig. 40-49). For the older descriptions, see T're+ 
viranus, Bau da. Arach. p. 41, Taf. IV. V., and 
Verm. Schrift. I. p. 11, Taf. I. fig. 4; and Brandt, 
Mediz. Zool. II. p. 89, Taf. XV. fig. 5, or Ann d. 
Sc. Nat. XIII. p. 184, Pl. IV. fig. 5. 
