THE ARMATURE OF ORBWEIiS : VISCID SPIRALS. 85 



ill order, in cases where the spiral scaffold is not easily accessible.^ T have 

 occasionally observed this action, but cannot certainly confirm tlie observa- 

 tion as habitual. At all events, the diagram will show this alternate move- 

 ment as it may be made between the radius 5 and radius G, or again be- 

 tween radius G and radius 7. 



From this point onward, while crossing laterally the lower portion of 

 the orb, and again while ascending, the striding movements which have 

 been described and illustrated by the previous figures become necessary. 

 Usually, however, upon the downward course, she drops from one 

 <^ . radius to another, and thus proves herself, like any human la- 



borer in mechanics and architecture, both able and willing to 

 make the best use of her time and strength by varying her ordinary habit, 

 and availing herself of natural conditions. I have described what is the 

 habitual course, as it may be seen by any careful observer. But there occur 

 exceptions, and I have sometimes had occasion to note the fact that some 

 spiders allow themselves to be so swayed by habit that they persist in 

 crawling around the sides of all the sections, instead of relieving them- 

 selves by the direct drop after the manner of their congeners. I suppose 

 that even in Spiderdom there is room for the ultra conservative consti- 

 tution. 



Mr. Black wall thus describes the mode of s[)inning the spirals, which 



correctly summarizes the detailed account which I have given. From the 



circumference of the orb the spider passes along a radius to the outer 



line of the s})iral scaffolding (having fixed a viscid thread to the end of 



the radius) — along which she goes to the adjoining radius, drawing out 



the thread, in her transit, with the claws of her hind leg nearest the 



circumference. She then transfers the thread to the claws of the other 



hind leg, and passing down the radius at which she has just arrived to the 



circumference, she places the foot of her liind leg })reviously emj)loyed in 



drawing out the threads on the point in the radius to whicli 



Black- ^^^^y filament is to be attached, and bringing her spinners to the 

 wall's De- , ,, , .. ' • i • i i- x 



scriDtion ^^ tliere makes it secure, ihe precise place in each radius at 



which to fix the thread is always ascertained by the situation 

 of the foot of the hind leg, and this is determined by touching with the 

 feet of those legs nearest the cireuiuference, the marginal line, or when 

 the structure of the net is further advanced, the last formed circumvolu- 

 tion of the viscid s})iral line.^ 



The spider advances, as we have seen, ])y a zigzag movement, [)artly 

 striding, partly swinging, catching alternately upon the oi)posing founda- 

 tion spirals and the next radius. Every radius crossed, at every crossing, 

 is touched as above described and the spiral causcMJ to adhere. In some 

 orbs whose radii number forty or fifty, and the si)irals as high as sixty, 

 the nuiidxT of attachments is very great — 2500 or 3000, and tliey are 



1 " 



Nets of Geometric Si)iders," page 183. 



