102 A NATURALIST IN HIMALAYA 



ment is made, and the filament anchored in the wrong 

 place. The diagram (Fig. 3) illustrates what has 

 occurred. Turn first to diagram a. Let w,x,y, z be 

 four adjoining segments. Let x be the experimental 

 segment, and let three turns, i, 2, 3, of the viscid 

 spiral be complete. I divide the innermost turn in 

 segment x. Now turn to diagram b. The spider 

 circles on laying down the fourth turn of its spiral 

 all round the snare. At length it reaches the radius 



a 



Fig. 3.— Loss of parallelism resulting from division of one turn 

 of viscid spiral in one segment. 



(a) Viscid S]nral divided in segment X. 



(J)) Result of spider's work. Loss of parailelisin in both X and Y. 



Arrow marks the direction of spider's circle. 



between z and y. Here all is well. It feels in its 

 measurement the turn it has last laid down and the 

 fourth line is parallel across segment z. It passes on 

 to the radius between x and jj/. It reaches forward to 

 feel line 3. But line 3 is gone, so it must touch line 2. 

 Its measurement is incorrect. The attachment is made 

 in the wrong place, farther out on the radius, and the 

 line drawn across segment y is out of parallel. The 

 spider passes on. It reaches the radius between w 

 and X. Stretching forward, it touches the correct line. 

 It anchors its filament in the right place. But the 



