XIII 



SPINNERETS 



325 



Under considerable magnification the legs of all Spiders 

 exhibit a number of minute organs, arranged with absolute 

 uniformity throughout the Araneae, and known as the " lyriform 

 organs." They consist of little parallel ridges of thickened 

 chitin, the slit between them being covered by thinner chitin. 

 They are eleven on each leg, and are distributed near the distal 

 extremities of each of the first six joints. Their function is 

 unknown, though some authors consider them to be organs of 

 hearing. 



The Spinnerets are normally six in number, and, except in 

 rare instances, are placed beneath the abdomen, near its apex and 

 immediately in front of the anal tubercle. 

 Their arrangement varies greatly, but 

 they can generally be recognised as 

 comprising three pairs, a posterior (or 

 superior) pair, a median pair, and an 

 anterior (or inferior) pair. 



In nearly all the Theraphosae the 

 anterior pair are absent, while the 

 posterior spinnerets are largely de- 

 veloped. In the Palpimanidae only 

 the anterior spinnerets are present. 

 When all six are found, the usual 

 arrangement is in the form of a rosette, 

 the median spinnerets being hidden by 

 tin- others in repose, but this disposition 

 is widely departed from. In Halinia 

 Agelenidae), for instance, they are 

 ranged in a transverse row at the end 

 of the abdomen, the posterior spinnerets 

 occupying the extremities of the row. 

 and the median ones the centre. 



These spinnerets are highly mobile 



J PIG. 181. Spinnerets oi Kpeira 



appendages, and additional play is giyeii diademata. A, Ventral view 



to their action by the presence of articula- 



lions. much resembling the " false "joints 



sometimes found on the legs, on the posterior and anterior pairs. 



They are always at least hi-art iculate, and sometimes present 



three or four joints. They arc movable turrets on \\hich are 



mounted the " fusulae " or projections where the bubea from the 





ol' 



: B. spinnei el 

 C. prnlilr. 



