74 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



FIG. 69. Spinning the initial radii. 



The trapezoidal foundation lines, x x, are woven within the basilar 

 part of the triangle thus formed. We have here the usual Foundation 

 Space, FS, and indeed might aptly apply that term to the entire Founda- 

 tion system. But it will be convenient, in webs of this form, to name 

 the inner side of the trapezoid, IFL, the Inner Foundation Lines, and the 



large exterior cords, ab, cd, the Outer Foun- 

 dation Lines, and the intermediate space, 

 OFS, the Outer Foundation Space. 



The inner foundation lines are of course 

 necessary to the construction of the orb 



under such circumstances, but 

 Use of In- , , T-i T -i 



ner Lines. * ey are P laml y so adjusted as 

 'not only to allow the nicest bal- 

 ance of the beautiful snare, but also to 

 afford the greatest power of resistance by 

 distributing the disturbing forces of wind 

 and struggling entangled insects along the 



elastic inner foundation lines. Webs of this character have less rigidity 

 and would seem to be better designed to endure, than those which are 

 directly attached to limbs and foliage. 



A foundation having been secured, the spider proceeds to place in 

 the radii. To this end a position is taken at or near the centre of 

 the orb, usually by dropping down from a top line, dragging 

 .. after her a thread which becomes the initial radius, Fig. 69, a. 

 ' At the central terminus of this radius a little ball of floss (H) 

 is formed by emitting a thick ray of silk or by gathering together into a 

 wad the many tentative lines with which the space within the frame is 

 frequently matted. This ball evidently serves as an 

 anchorage for the radii and perhaps also as a guidon 

 for the animal herself. Sometimes as the work pro- 

 ceeds and the strain of the new laid radii is felt 

 upon the centre, the bit of floss is pulled out into 

 an irregular frayed mass with interlacing filaments, 

 as at Fig. 70, which shows a hub of a snare of 

 Epeira vertebrata arrested when nine radii had been 

 spun. The spider hung at the centre, and the posi- 

 tions of the feet in their order (first, second, etc.) are indicated by the 

 numerals. 



The spider may now proceed in two ways: first to drop downward 

 from H along c, to the foundation line, and attach thereto the thread, 

 which is done by touching the spinnerets to the point of attachment, the 

 natural viscidity of the exuded silk causing it to adhere. This gives the 

 second radius. Thence the spider returns along c to the centre H, and 

 ascends a, to form the third radius Hk or Hi. If, however, the tentative 



