CONSTRUCTION OF AN ORBWEB. 61 



Dr. ITiilsc, as early as A. J). 1070, noticed the lidbits of spiders to make 

 various anchorages of their drag line as they moved along. He thus wrote 

 to Mr. Ray : " They will often fasten their threads in several places to the 

 things they creep np : the manner is by beating their bums or tails against 

 them as they cree^) along. This line will express the way : — 



By this frequent beating in of their thread among the asperities of the 

 place where they creep, they either secure it against the wind, that it is 

 not so easily blown away ; or else whilst they liang by it, if one stitch 

 break, another holds fast, so that they do not fall to the ground." ^ 



In this way the Orbweaver proceeds, with more or less variation, until 

 she has described the irregular polygon which forms the foundation of her 



snare. ^ Each of these boundary lines, according to Black wall's 

 Prnne observation, is composed of five, six, or even more united 

 ■ • threads.^ It is always sharply distinguished by its thickness and 



strength, and often by its color, from the other lines of tlie snare. 

 The ui)per foundation line is quite commonly much the strongest. The 

 framework thus formed is braced by various cords passing diagonally from 

 line to line across the corners, and some- 

 times also by numerous threads attached to 

 surrounding objects. The entire foundation 

 thus hangs taut, and presents a framework 

 having the requisite degree of strength and 

 elasticity upon and within which to suspend 

 the true snare. 



This work is not always done rapidly and 

 as tliough by an engineering instinct that fig. 59. Dragline and anchorage 

 readily perceives the quickest and most ad- magm 



vantageous sites and courses. Often there is much preparatory pioneering ; 

 the laying out or dragging out of tentative lines which appear to be to no 

 purpose; a groping or "feeling" the way, so to speak, toward tlie best loca- 

 tion, and at last the seeming accidental determination of the frame lines. 

 Of course, even under such behavior there must be a general instinctive 

 niovomont in the direction of the polygonal or triangular outlines wliich 



are the prevailing forms one sees. It has been said thai the 

 Intelli- spider seems careless about the shape of the area which the 

 Selection ^^'"^^^^'^tion lines inclose.^ But the fact that these two forms do 



prevail well nigh universally, places the architect's action outside 

 the pale of mere chance. Moreover, examples are frt([iuiilly t'uuud of 



^ Correspondence of Ray, page 58. 



2 See an article by the author in "Our Continent," Philadelphia. September 27th, 1S82. 



3 Black wall, Zoolo^'icul .IdUiiial, Vol. V., 1S.S2-4, ]uij:e 1S2. "On the Construction nf tlic 

 Nets of ( Jeoiuctric Spiders." 



•* Introduction to Entomology, Kirby tS: Spcncc, \'ul. 1., Set Xlll., l)age 411. 



