SPINNERETS 



325 



Under considei'able 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 l)y 

 the others in repose, but this disposition 

 is widely departed from. In Hahnia 

 (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 

 appendages, and additional play is given 

 to their action by the presence of articula- 

 tions, much resembling the " false " joints 

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

 They are always at least bi-articulate, and sometimes present 

 three or four joints. They are movable turrets on which are 

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



Fig. 181. — Spinnerets of Epeira 

 diademata. A, Ventral view 

 of Epeira ; B, spinnerets 

 magnified ; C, profile. 



