XIII 



STRIDULATING ORGANS 



327 



spiders possessing them certainly do not seem to form a 

 natural group. 



Stridulating Organs. When Arthropod animals are capable 

 of producing a sound, the result is nearly always obtained by 

 " stridulation," that is, by the friction of two rough surfaces 

 against each other. The surfaces which are modified for this 

 purpose form what is called a " Stridulating organ." Such 

 organs have been found in three very distinct Spider 

 families, the Theridiidae, the Sicariidae, and the Aviculariidae. 

 Hitherto they have only been observed in three positions- 

 cither between the thorax and abdomen, or between the 

 chelicerae and the pedipalpi, or between the pedipalpi and 

 the first legs. 



Tu the Sicariidae and the Aviculariidae, the sounds have 

 been distinctly heard and described. Those produced by the 

 Theridiidae would appear to be inaudible to human ears. 



Westring l was the first to discover (1843) a Stridulating 

 organ in the small Theridiid spider Asagena phalera/. The 

 abdomen, where the pedicle 

 enters it, gives off a chitinous 

 collar, which projects over 

 the cephalothorax, and has 

 the inner surface of the 

 dorsal part finely toothed. 

 When the abdomen is raised 

 and depressed, these teeth 

 scrape against a number of 

 fine striae on the back of 

 the posterior part of the 

 cephalothorax. 



organ has been since found 

 in various allied spiders, of 

 which the commonest Eng- 

 lish species is Wf<tti><1n bipunctata. In this group it is generally 

 possessed by the male alone, being merely rudimentiiry, if present 

 ;ii all, in the female. 



In 1880 Campbell' 2 observed that in some of the Theridiid 

 Spiders of the genus Lephthyphantes, tin- outer surface of (lie 



4 -i Fi<;. 183. Stridulating apparatus of ,sy<v//,,,/,/ 



bipunctata, 6. Much enlar-ed. A, 



and toothed abdominal socket ; B, striated 

 area on the cephalothorax ; C, profile <>!' 

 the Spider, > ;".. 



1 Nul. ///.s-/. 7Yr/s,9/r. iv., 1843, \>. 349. 

 - J. Linn. ,bW. xv., Ib81, p. 155. 



