THE SPINNING ORGANS. 



39 



They are placed in a mass just above the spinnerets, and within their 

 bases and the abdomen, and along the venter forward and laterally. See 

 Fig. 30. The pyriform glands, which are smaller and very much the most 

 numerous, are arranged in five roundish clusters, about two millimetres in 

 diameter in A. cophinaria, each corresponding to one of the exterior spin- 

 nerets, one cluster being devoted to the two middle spinnerets, al- 

 ^^ though even in this case the clusters can be separated into two. 



N , ' The number of glands precisely corresponds with the number of 

 spinning spools and spigots. Bucholz and Landois give about 

 seven hundred for Epeira diademata and they are as numerous in Argiope 

 cophinaria. Mr. Blackwall expresses the opinion that the total number of 

 spinning spools does not greatly exceed a thousand, even in adult females 

 of Epeira quadrata, whose weight is about twenty grains, and in many other 

 species it is smaller. As the spools correspond in number with the glands, 

 this gives an indication of the number of silk glands within our best known 



FIG. 30. Partly diagramatic view of the location of the spinning organs in Argiope 

 cophinaria. spn, spinnerets ; py.g, pyriform glands ; cy.g, cylindrical glands ; tr.g, 

 treeform glands ; ep, epigynum ; gl, gills : E, eggs ; al.c, alimentary canal ; a, anus. 

 Th figure is a composite one. 



Orbweavers. Each gland terminates in a long, delicate duct, and one duct 

 enters one of the spools ; a distinct duct belongs to every spool, without any 

 connection, as a rule, with other ducts or glands. 



Under the microscope the liquid silk can be seen very distinctly within 

 the glands, and presents the appearance of minute, yellowish, translucent glob- 

 ules of thickish oily or viscous substance. Some of the glands of Argiope 

 cophinaria appear to contain material which is rather smoother and of a 

 lighter color than that above described. The contents of some 

 glands in this species have a reddish brown color, which indicates 

 that they supply the brown silken padding that envelops the 

 eggs of this species and lie just within the outer cocoon case. Where the 

 glands have been broken, or the contents spilled on the mounting cover, the 

 liquid silk generally shows stringy or fibrous, but sometimes maintains the 

 globular appearance retained within the gland. It is very probable that 



