388 



THE ARACHNOIDAE. 



<§»315. 



n. Organs of Special Secreiio7is. 



^ § 315. 



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

 excreted through the extremity of a hollow claw. With the PhryniJac, the 

 Araneae, and some Acariiia, there are two such glands in couiniunication 

 with the terminal hooks of the cheiiceres. They have been often taken for 

 salivary organs. With the Trombidina, there are, on each side of the 

 cephalothorax, two small, flexuous, coloi'less, glandular tubes, which, at 

 their anterior extremity, are dilated, each, into a cylindrical, thin-walled 

 poison-resei'voir. From this reservoir arises a long, narrow canal, which 

 runs to the cheiiceres. <*' 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 

 cheiiceres, 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 cheiiceres.'** 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 diiferent 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 

 follicles, aggregated in groups of hundreds, and having short excretory 



1 The two poison-glands of the Trombidium ho- 

 losericeiim, and Rhyncholophua phalangin'ides, 

 have the form of a ring with a small opening. 

 Treviranus (Verm. Schrifl. I. p. 4S, 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. Du^is (Ann. d. Sc. 

 Nat. III. p. 10), on the contrary, perceived their 

 true relation to the cheiiceres. 



'- 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, Clubinna 

 and Mygale ; with Salticus-, they present obscure 

 transverse lines, so that I am undecided whether 

 they belong to the first or to the second of these 

 categories. 



■"> With Mygale, these glands are entirely con- 

 ceiled in the basilar article of the cheiiceres. 



•4 Trei'iranii.i, Bau d. Arachn. p. 31, Taf. II. 

 fig. 21, 2-2 i Lyonet, loc. cit. p. 397, I'l. XX. fig. 



16, 17 ; Brandt, Mediz. Zool. II. Taf. XV. fig. 6, 

 or Ann. d. Sc. Nat. XIII. PI. IV. fig. 2 ; and 

 Wasrnann, loc. cit. p. 19, fig. 25, 26. For the in- 

 timate structure of these glands, see Meckel, in 

 Muller's Arch. 1S46, p. 35. 



5 Miiller, in MeckePs 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 curopaeus, I have seen this layer covereil, 

 externally, with a stratum of cylindrical cells. 



'' The Mygalidae have two pairs of these papillae, 

 or spinnerets, instead of six, the usual luimber. 



- I speak here upon the careful investigations of 

 H. Meckel {Mu/ler's Arch. 1846, p. 50, Taf. III. 

 fig. 40-49). For the older descriptions, see Tre- 

 viranus, Bau d. Arach. p. 41, Taf. IV. V., and 

 Verm. Silu-ift. I. p. 11, Tal'. I. fig. 4 ; and Brandt, 

 Mediz. Zool. II. p. 89, Taf. XV. fig. 5, or Ann d. 

 Sc. Nat. -XIU. p. 184, PI. IV. fig. 5. 



