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 tlius formed. We have here the usual Foundation 

 Space, FS, and indeed might ai)tly 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 sucli circumstances, but 



T . 'they are plainly so adiusted as 

 ner Lines. 11 



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 tliose 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 



xi-^^^j"^^fter her a thread which becomes the initial radius, Fie. 69, a. 

 the Radii. . p i • i j & ' 



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 

 frecjuently 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 l)it of floss is pulled out into 

 an irregular frayed mass with interlacing filaments, 

 as at Fig. 70, which shows a hulj 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 pow proceed in two ways: first to drop downward 

 from 11 ;Uong c, to the fouiulation line, and attach thereto tlie thread, 

 which is done ])y 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 tlie third radius Ilk or Ili. If, liowever, the tentative 



Fig. 70. Pulled out guidon. 



