THE SPINXIXG ORGANS. 



35 



su 



lSF 



about equal in lengtli. Tn form these organs are somewhat conical and 



cylindrical, widened at the base and gently sloped or flattened at the tips. 

 The three pairs differ somewhat in appearance and size, the mid- 

 , die pair being shorter and less in size and more closely approx- 



imated. The posterior and anterior spinnerets have two joints 



(Bucholz and Landois) ; the middle ones are unjointed cones. ^ They are 



movable, particularly the posterior and anterior pairs, articulating with the 



integument of the body, and can 



be closed in upon each other until 



the tips touch at the spinning fields, 



as when one closes the thumb upon 



the four fingers of his hand. The 



spinning fields, Fig. 21, SF, are 



those portions of the tii)s and sides 



of the spinnerets on which are 



placed the sessile tubes out of 



which the silk passes. 



In repose the spinnerets are gen- 

 erally closed (Fig. 21), forming a 



sort of rosette of five divisions; but 



when the spider is engaged in ac- 

 tive operations, the posterior and 



anterior spinnerets are thrown well 

 back, and the two middle 



1. Poste- Qj-^gg Qp0j^ ^^p^ and thus, 



rior Spin-, . .^ ^ n 



, to quote the language or 



nerets. ^ t. ^ 



Duges, " this singular flow- 

 er unfolds." The posterior spinner- 

 ets (Figs. 21 and 23, Vp are well 

 separated from each other, and lie 



directly forward of the semilunar Fig. 23. Posterior spinneret of Ep. diaderaata, greatly 



1 • /T-T Q-( \ rpi magnified, su, sutine between joints; SF, spinning 



anal COVernig [lUg. Zl, acj. iney field ; bb, branched bristles ; sb, simple bristles ; sp, 



are movable horizontally toward spigot spool; l.ss, long spinning spools; s.ss, short 



, . , , 1 , , T • 1 1 spools. (After Bucholz and Landois.) 



each other, so that their long oval 



spinning fields approximate and, indeed, may be said to lie upon the cor- 

 responding middle spinnerets. They may be described as thumb shaped 

 organs ; are of a long, cylindrical form, and towards the free end are con- 

 ically rounded. The terminal joint is divided from tlie base by a suture. 

 Fig. 23, su, which extends along the inner and hinder edge, much farther 

 than on the opposite edge, so tluit the spinning i'whl extends on that face 

 much farther towards the base. 



^ Mccki'l and Oeffinger both atliilmtr tliivc' joints to tlii' i)()st(.-rior and antcridr, and two 

 to the niitldic spinnerets. 



^ To juvvent ronfiision and tlic nuiltii>licatioii of reference.s t<i fiirnreis the same letter 

 ing is preserved for like organs and part.s thereof in all tlie anatoniii-ii tigures. 



