ARACHNIDA. 



4o7 



arrangement of the fibres of the contractile tunic. The duct (b) tra- 

 verses the basal joint of the mandible and the cavity of the fang (c), 

 and terminates in a fissure on its convex surface near the point. In 

 the true Aranece, the Clubiones, and the Lycozw, the poison glands 

 extend into the cephalothorax ; but in the bird-spiders {Mygale) 

 they are limited to the mandibles. It is probable, therefore, that 

 the effects of a Avound occasioned by these gigantic spiders may be 

 exaggerated : those species of our native spiders, which are most for- 

 midably armed, cause little or no inflammation in piercing the human 

 skin ; but their poison seems to take fatal effect upon insects. The 

 mechanical laceration, and the sucking out their juices, must, how- 

 ever, be taken into the account of the lethal powers of the spiders"as 

 exercised upon their entrapped prey. Litmus paper pierced by the 

 mandibular hooks of irritated spiders becomes red as far as the 

 emitted fluid spreads, showing tiie poison to be acid. 



The organs which secrete the material of the web are lodged in 

 the posterior part of the abdomen, and in Epeira fasciata, whicli 

 is remarkable for the large size of its web, they occupy, when in full 

 activity, about one fourth of the abdominal cavity. They present 

 the form either of slender and more or less branched tubes, or of di- 

 lated sacs, the excretory ducts of which terminate upon projecting 

 jointed organs at the posterior extremity of the abdomen, called 

 spinnerets {Jig. 172, ii). 



In the Clubiona atrox the glands consist of four larger and nume- 

 rous smaller tubes : two of the larger branched 1 "0 

 tubes are twice the size of the other pair. 

 In the genus Pholcus (Jig. 170) the organ is 

 reduced to a more simple condition ; it con- 

 sists of six vesicles of different shapes and 

 sizes ; two {q) are large and elongated ; they 

 occupy the middle of the under part of the 

 abdomen, and their slender ducts are con- 

 tinued in a tortuous course to the spinnerets ; 

 two others (r) are also elongated, but are 

 smaller than the preceding ; the remaining 

 two are spherical {s). Tlie duct of each of ( 

 these glands terminates upon its appropriate 

 spinneret, and there are consequently six of 

 these organs. 



Mygale avicularia has only four spinnerets, 

 and in Mygale cementaria tw^o of them are 

 imperforate. Clubiona atrox and some species of Drassns have eight 

 spinnerets ; the two accessory ones being situated in advance of the 



Pholcus. 



