38§ THE ARACHNOIDAE. *§> 315. 



II. Organs of Special Secretions. 



§ 315. 



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 less into the ce2)halothorax,*'^' 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 ^he 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 flve kinds of these glands may be dis- 

 tinguished, although not always simultaneously in the same individual. 

 The threads have probably difi"ercnt 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- 16, 17 ; Brandt, Mediz. Zool. II. Taf. XV. fig. 6, 



loxericeum, and Rhyncholophus phalangioides, or Ann. d. Sc. Nat. XIII. PI. IV. fig. 2 ; and 



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



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



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



glands with the first mentioned of these animals ; 5 Miiller, in MeckeVs Arch. loc. cit. p. 52, Taf. 



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



them for salivary glands. Duges (Ann. d. Sc. portion of these glands which is surrounded l>y 



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



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



U It is remarkable that these muscular fasciculi cles enveloping the muscular layer. In fact, with 



present such different histological characters. I Scorpio europaeas, I have seen this layer covered, 



have seen them distinctly striated with Li/co.ia, externally, with a stratum of cylindrical cells. 



Drassus, Tegenaria axiA Micryphantes. They fi The Mygalidae have two pairs of these papillae, 



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

 and My gale ; with Snlticiis, they present obscure ' ^ I speak here upon the careful investigations of 



transverse lines, so that I am undecided whether H. Meckel (Mailer's Arch. 1846, p. 50, Taf. III. 



they belong to the first or to the second of these fig. 40—19). For the older descriptions, see Tre- 



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



3 With My gale, these glands are entirely con- A'erm. Schrift. I. p. 11, Taf. I. fig. 4 ; and Brandt, 

 ceiled in the basilar article of the cheliceres. Mediz. Zool. II. p. 89, Taf. XV. fig. 5, or Ann d. 



4 Treviranus, Bau d. Arachn. p. 31, Taf. II. Sc. Nat. XIII. p. 184, PI. IV. fig. 5. 

 fig. 21, 22 ; Lyonet, loc. cit. p. 397, PI. XX. fig. 



