THE SPINNING ORGANS. 



35 



about equal in length. In 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 niid- 

 ^ , ' 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 tips 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- QQgg Qpgj^ ^^p^ j^j-^j thus, 

 nor P "^^ ^Q quote the language of 



Duges, " this singular flow- 

 er uirfolds." The posterior sjiinner- 

 ets (Figs. 21 and 23, P)^ are well 

 separated from each other, and lie 

 directly forward of the semilunar 

 anal covering (Fig. 21, ac). They 

 are movable horizontally toward 

 each other, so that their long oval 

 spinning fields approximate and, indeed, may be said to lie ui)on the cor- 

 responding middle spinnerets. They may be described as tluimb shaped 

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

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

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

 than on the opposite edge, so that the spinning field extends on that face 

 much farther towards the base. 



Fig. 23. Posterior spinneret of Ep. diademata, greatly 

 magnified, su, sutine between joints ; SP, spinning 

 field; bb, branched bristles; sb. simple bristles; sp, 

 spigot spool ; l.ss, long spinning spools ; s.ss, short 

 spools. (After Bucholz and Landois.) 



1 Meckel and Oeffinger both aUribute three joints to the posterior and anterior, and two 

 to the middle spinnerets. 



= To prevent confusion and the ninltiplication of references to figures the same letter- 

 ing is preserved for like organs and parts thereof in all the anatomical figures. 



