ARACHNIDA. 



261 



these gigantic spiders may be exaggerated : those species of our 

 native spider which are most formidably armed, are unable to inflict a 

 wound on the human skin by any means so painful as the sting of a 

 bee, but their poison rapidly takes fatal effect upon insects. 



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

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

 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 

 spinnarets. (fig. 112. a.) 



In the Cluhione atrox-^ the glands consist of four larger and nume- 

 rous smaller tubes : two of the larger branched tubes are twice the size 

 of the other pair. In the genus Pholcus 

 {JiQ' 113.) the organ is reduced to a more 

 simple condition ; it consists 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 continued in a 

 tortuous course to the sj)innerets ; two 

 others (r) are also elongated, but are 

 smaller than the preceding ; the remaining 

 two are spherical is). The duct of each 

 of these glands terminates upon its ajDpro- 

 priate spinneret, and there are conse- 

 quently six of these organs. 



The Mygale avicularia has only four 

 spinnarets, and in the Mygale cementaria 

 YYyQicns ^^^ ^^ them are imperforate. Six, how- 



ever, is the ordinary number of spinnarets 

 in the spiders, two of which are longer than the others. The secre- 

 tion does not issue by a simple outlet, but by a multitude of micro- 

 scopic pores_, which, in the shorter pairs of spinnerets, are prolonged 

 from the terminal surface upon minute processes. If you throw a 

 little dust upon the web of any of the orbitele spiders, of the Epeira 

 diadema for example, you may observe that it adheres to the spiral, 

 but not to the radiated, threads. Lyonnet supposed that the adhesive 

 threads issued from tubes, and the others from sessile orifices. The 

 secretion is a glutinous fluid, insoluble in water, and which quickly 

 dries in air ; some species, as the Argyroneta aquatica^ spread their 

 nets habitually under water. 



s 3 



