COMPOSITE SNARES AND SECTORAL ORBS. 



139 



three-eighths inch, one-fifth the orb space. These were all webs of young 

 spiders. It will thus be seen that there is no fixed rule by which 

 Triaranea is guided in this outlay of her web, and that she allows herself 

 a wide range of variation, altliough the greater number of orbs show 

 a sector of about one-fifth the orb space. 



Through the open sector passes the free radius or trapline, for such 



Trapline. 



Fig. 124. Fig. 125. 



Illustrations of the orientation of the trapline, and width of 



the open sector. 



it is, its use being i)recisely that of the trapline fig. 126. Beii shaped tent in which 

 in full orb making spiders. Near the point of '^^ ''^p"°^ terminates, 



attachment to the hub this is deltated, diverging into several lines that 

 are fastened at various points to the meshes of the hub. The 

 other end of the trapline enters a little bell shaped silken tent 

 swung amid a rctitelarian maze, where it is held by the spider. (Fig. 126). 

 Sometimes several spiral lines will cross the upper part of the open 

 sector (Fig. 127) ; again one may see the variation shown at Fig. 128, where 

 two radii (dr dr) detached from the hub (H) are lifted out from the 

 plane of the orb, leaving an open space (O) through which the trapline 

 (T) passes. Another variation differs from this in having but a single de- 

 tached radius (dr) to which cross loops (cl) pass from the marginal radii 

 R, R. (Fig. 129.) When weav- 

 ing in the spirals this spider does 

 not pass entirely around the orb, 

 as is the case with the full orb 

 makers in the major part of their 

 snare, but moves back and forth 

 between the radial borders (Fig. 

 125, c and d) of the open sector, 

 spinning her spirals in successive 

 horseshoe loops. This 



, is the method observed 



Lioops. 



by Zilla, and all sectoral orb makers in fact. The necessity for it 

 is at once apparent. Of course, in this case the term " spiral " has only 

 a technical application to tliese lines. (Fig. 130.) 



The number of both spirals and radii varies greatly. The latter are 

 more numerous, often far more numerous below than above the hub, 

 which frequently is situated well above the geometric centre of the orb. 

 Thus, in an orb six inches wide by seven long the spirals in the upper 

 part of the snare numbered nineteen, in the lower thirty-two. The lower 



Fig. 128. Fig. 129. 



Variations in the open sector ; detached radii. 



