46 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



whifli the spider's spinningwork is composed. The ordinary spiiiniii,u; 

 spool is i\ hollow, cylindrical, chitinous formation, and consists of two 

 joints : thst, a shorter or longer hasal cylinder, bj, whose walls are strongly 

 brown colored ; and second, a much smaller and transparent ter- 

 Spinnmg j^^jj^.j jq^j-^^^ ^j^ which terminates in a very fine point, provided 

 P°° ^" with a minute opening. The spools in which the pyriform 

 glands terminate, s.ss and l.ss. Fig. 24, stand in large number on all the 

 spinning fields. They are not alike in form of the several spinnerets, 

 and those of the anterior spinneret especially, are r^uite differently con- 

 structed from those of the posterior pairs. 

 On those spools of the posterior spinnerets 

 which receive pyriform glands, the basal 

 joint (Fig. 39, bj) forms everywhere a reg- 

 ular cylindrical tube of even 

 yri orm ^]jj(.],j^ggg w'hich seems to be 

 Spools. , , , , • , 



obliciuely cut at the exterior end 



where the terminal joint is united to it. 

 This interrupted space is, as Fig. 39 (i.s) 

 shows, a very little flat in the middle, and 

 towards the edge slightly curved. The base 

 of the tube is joined to the surface of the 

 si)inneret by a ring formed enlargement, 

 and, as elsewhere, bristles and hairs with 

 chitinous rings are seated upon the skin. 

 Into the base of each spool enters a 

 single duct of a pyriform gland, and this 



the anterior spinneret. X 2000. Fig. 41. '^Uct CaU be folloWed aS a straight tubc 



Spinning cone or spigot into which a cylin- {q tbc Cud SpaCC of the base of tllC SpOol, 

 drical gland empties. The whole taken i - , ± • ± i i • 



from the apex of the middle spinneret. wllCrC it CCaSCS tO CXlSt RS a CaiUll, and IS 



X 2000 times, bj, basal piece; c, circumfer- nicrgcd into the cavity of the terminal 



ence or ring of the chitinous wall of the . . 



joint. 



The terminal joint (tj) is in the larger 

 tubes, about half the length of the basal 

 joint, bj, and sits precisely in the centre 

 of the summit of the basal joint. The 

 terminal joint is hollow, gradually diminishes, and terminates in a very 

 fine, round oj^ening at the tip. The thickness of a single thread, coming 

 from this spinning spool, would be about 0.001 mm., or one twenty-five- 

 thousandth part of an inch. This form of spinning spool undergoes 

 changes at different places of the spinning field, caused by the basal cylin- 

 der varying in length. The central parts of the spinning field especially 

 are covered with very short spools. The terminal joint, however, remains 

 unchanged in length, notwithstanding the varying lengths of the basal 

 joint. (Fig. 39.) 4. 



Fig. 39. Fig. 41. Fit;. 40. 



Fig. 39. Spinning spool of the usual form 



from the posterior spinneret, and connected 



with pyi'iform glands. Multiplied greatly, 



2000 times. Fig. 40. Spinning spool from 



basal piece, constituting a ring formed 

 chitinous thickening on its apex ; em. the 

 exterior membrane of the chitinous wall 

 of the duct, du, with vertical striation; im, 

 inner membrane of the duct passing into 

 the canal of the basal piece. 



