46 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



which the spider's spinningwork is composed. The ordinary spinning 

 spool is a hollow, cylindrical, chitinous formation, and consists of two 

 joints : first, a shorter or longer basal cylinder, bj, whose walls are strongly 

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

 ' minal joint, tj, which terminates in a very fine point, provided 

 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 quite 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 

 g , thickness, which seems to be 

 obliquely 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 

 spinneret 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 

 with pyriform glands. Multiplied greatly, single duct of a pyriform gland, and this 



2000 times. FIG. 40. Spinning spool from -. , - n . v, 



the anterior spinneret. X 2000. FIG. 41. duct Can be followed as a Straight tube 



spinning cone or spigot into which a cyiin- to the end space of the base of the spool, 



dncal gland empties. The whole taken , . ... 



from the apex of the middle spinneret, where it ceases to exist as a canal, and is 

 x 2000 times, bj basai piece ; c, circumfer- merg ed into the cavity of the terminal 



ence or ring of the chitinous wall of the . J 



basal piece, constituting a ring formed JOlllt. 



rpi terminal ioint (*\\ iq in thp 

 (1 J O1 W 



C 



du 



' im 



FIG. 39. FIG. 41. FIG. 40. 



FIG. 89. Spinning spool of the usual form 



from the posterior spinneret, and connected 



chitinous thickening on its apex; em, the 



exterior membrane of the chitinous wall 



of the duct, du, with vertical striation; im, tubes, about half the length of the basal 



inner membrane of the duct passing into 4 i j , i .-, 



the canai of the basai piece. J om t, 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 opening 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.) 



