104 A NATURALIST IN HIMALAYA 



ment may touch one of these little tags and, believing 

 it to be the spiral, may anchor its new filament correctly. 

 Moreover, the experiment seldom succeeds when the 

 spider is working at the inner and smaller turns of the 

 spiral. This, I think, is due to the fact that here the 

 spider can move directly across from radius to radius 

 without deviating its course, or can stretch directly to 

 its point of attachment from its bridge on the tempo- 

 rary spiral, so that the previous turn of the viscid 

 spiral is here much less important as a means of 

 measurement than in the earlier and more external 

 part of its construction. 



But these difficulties avoided, we reach a clear 

 conclusion. Each turn in the viscid spiral is the 

 essential guide to the accuracy of the next turn. For 

 if the one be divided then the next is incorrect. And 

 from the way the spider feels with its leg at each 

 attachment, there is strong reason to think that the 

 fore leg is the organ on which the accuracy depends. 

 These experiments strengthened my belief that the 

 fore leg was the instrument employed by the spider 

 to draw line parallel to line. 



But a third experiment overcame all doubts. I 

 found a snare in which the spider had completed the 

 outermost turn of the viscid spiral. With a fine 

 pair of scissors I succeeded in cutting off the tips of 

 the spider's two fore legs. By this operation I had 

 removed what I believed to be the sensitive organs 

 of measurement, and I was eager to detect whether 

 the spider could continue the construction of the 

 snare after so serious a mutilation, and, above all, 

 if it could still ensure the parallelism of its lines. 

 Immediately after I had nipped off the tip of the 



