THE SriXXINU ORGANS. 



37 



The S2:)innercts articulate 



obliquely from the outer side 



and the front, inward and 



backward, so that their ti})S 



ai)proximate the correspond- 

 ing spinning helds of the mid- 

 dle spinnerets. The base is 



covered on both of its side 



faces with many rows of Ijris- 



tles (Fig. 25, b) ; it is divided 



from the terminal field by a 



suture, su, and a brown chit- 



inous zone, z. The terminal 



joint is cap-shape, and is only 



partially occupied as a spin- i^^^ 



ning field. 



On the top of the spinning 



field are from sixty to seventy 



very short spinning spools, 



s.ss, and a spinning spigot, 



connected with a cylindrical 



gland, Fig. 25, sp.c. The base 



of these spigots is surrounded 



by a })air of chitinized stripes, 



which originate in the cliit- 



inous zone, z. Close to this 



place is inserted a very strong 



and long sinew, sw, which unites with the chitinous border of the spin- 

 ning field at the furrow (su) between the base and the terminal joint. 



This sinew passes beyond the root of the spinneret into the strong, motor 



muscle, ms, which controls the movement of 

 the spinneret towards its fellows. Within the 

 Ijl bases of the spinnerets are bundles of muscles 

 which contribute both to the general move- 

 ment of the spinneret and to the movement 

 of the individual spools on the tip. On the 

 chitinous edge of the spinning field is a single 

 row of strong bristles, br. 



On examining the spinnerets witli a lens 

 of ordinary power, tlir tii)s or si»iiniing fields 

 are found to be covered with a great number 



Fig. 26. View of the spinning spools of . . 



Argiope cophinaria, as they appear in of fiuc moVablc Spinning tubcS, already men- 

 clusters a, short spools; c, long spools; tioned, known as si.inning spools (Fig. 20), 



b, a small cluster; tj, terminal joint; ' ' o i \ o /; 



bj, basal joint. whicli are rcguliirly tlis})0.sed over the surface. 



Fig. 25. Anterior spinneret, magnified largely, z, brown chit- 

 inous zone that bounds the spinning field ; sw, sinew of the 

 bending muscles of the anterior spinning wart ; du.c, duct 

 from cylindrical spinning glands ; sp.c, spigot discharging cy- 

 lindrical gland ; sp.t, spigot of trceform gland ; s.ss, spinning 

 spools of pyriform glands. (Bucholz and Landois.) 



