388 THE ARACHNOIDAE. § 315^ 



II. Orgayis of Special Secretions. 



§315. ■ 



Very many Arachnoidae have Poison-glands, the product of which ia 

 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 less 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 difl'erent 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 tw^o poison-glands of the Trombidium ho- 16, 17 ; Brandt, Mediz. Zool. II. Taf. XV. fig. 6, 



losericeum, and Rhyncholophus phalangMidr.s, or Ann. d. Se. Nat. XIII. PI. IV. fig. 2 ; and 



have the form of a ring with a small opening. IVasmann, loe. cit. p. 19, fig. 25, 26. For the in- 



Treviranus (Verm. Schrift. I. p. 48, Taf. VI. fig. timate structure of these glands, see Meckel, ia 



34) lias described only very imperfectly these MiUler\'s Arch. 1846, p. 35. 



glands with the first mentioned of these animals ; 5 Müller, in Meckel's Arch. loc. cit. p. 52, Taf. 



and not having seen their e.Kcretory ducts, he took I. fig. 7, 8. Serres (loc. cit. p. 90) regards the 



them for salivary glands. Duges (.\nn. d. Sc. portion of these glands which is surrounded hy 



Nat. III. p. 10), on the contrary, perceived their muscular fibres, as a reservoir of poison, and that 



true relation to the chelicere.s. this last is secreted by innumerable glandular folli- 



'^ It is remarkable that these muscular fasciculi cles enveloping the muscular layer. In fact, witli 



present such different histological characters. I Äcor/Ji'o e?«ro/)ae«s, I have seen this layer covered, 



have seen them distinctly striated with Lycosa, externally, with a stratum of cylindrical cells. 



Drassus, Tegenaria auA Micryphantes. They H The .Mygalidae have two pairs of these papillae, 



are smooth with Epeira, Thomisus, Clubiona or spinnerets, instead of six, the usual number, 



and Mygale ; with Sallicus, they present obscure ^ 1 speak here upon the careful investigations of 



transverse lines, so that I am undecided whether H. Meckel {Mutter's Arch. 1843, p. 50, Taf. HI. • 



they belong to the first or to the second of these tig. 40-19). Kor the older descriptions, see Tre- 



categories. virantis. Hau d. Arach. p. 41, Taf. IV. V., and 



'■i With Mygale, these glands are entirely con- Verm. Schritt. 1. p. 11, Taf. I. fig. 4 ; and Brandt, 



ceiled in the basilar article of the cheliceres. Mediz. Zml. 11. i>. S!i, Taf. XV. fig. 5, or Ann d. 



* Treviranus, Bau d. Arachn. p. ol, Taf. II. Sc. Nat. .VUI. \<. 184, I'l. IV. fig. 5. 

 fig. 21, 22 j Lyonet, loc. cit. p. 397, 1*1. XX. fig. 



