THE AERIAL WEB SPINNERS 177 



down straight lines an inch or two long, then cross them by over- 

 spinning shorter lines. These principal framework lines need only 

 to be lengthened, and they become the radii of the orb weaver, 

 which likewise puts down its rays from the hub outward. The 

 primitive radii were numerous, closely spaced, and probably fre- 

 quently branched so that the interval between adjacent radii at the 

 edge of the web was little greater than that near the center. (The 

 silk spiders still use this device to produce their strong net webs.) 

 All these framework lines were originally dry draglines, and remain 

 dry in all spiders. The webbing that crossed the radii was at first 

 dry or very slightly viscous, a condition reflecting both the pres- 

 ence of only small amounts of sticky silk and the failure to concen- 

 trate it in heavier drops. 



In the early orb weavers, the webbing over the dry framework 

 corresponded to the viscid spiral of the higher orb weavers. The 

 tremendous accomplishment that it represented was the formalizing 

 of an irregular maze into a series of regular lines crossing the radii 

 at nearly right angles. The first regular lines were probably series 

 of curves that covered a sector of the whole, then larger loops oc- 

 cupying half the circle, and finally complete spirals that produced 

 the relatively symmetrical orb web. These lines may well have been 

 long dry rods covered with a viscous coating. At this time the 

 formal round platform, entirely enclosed within the maze of criss- 

 crossed threads, was still only a platform on which insects dropped. 

 By slow stages the accompanying mazes, especially the one above 

 the platform, were lost, but only in the highest orb weavers are 

 they gone completely and even here their vestiges may still be 

 seen in the tangle that leads to the retreat and the hidden egg sac. 

 The gradual inclination of the orb, and the final near vertical posi- 

 tion, were inevitable refinements. 



The evolution of the orb web progressed hand in hand with 

 changes in the silk and in the spiders themselves. The silk glands 

 gradually became a voluminous part of the abdominal contents, and 

 were able to produce silks of differing properties. (In some modern 

 forms there are more than six hundred separate glands producing 

 five different kinds of silk.) Viscid silk was manufactured in larger 

 quantities, and, when concentrated on the spiral lines, changed the 

 round platform from a stopping net to an adhesive snare. As these 

 early spinners developed, various groups branched off the main line 

 to become sidetracked at different development levels. Some come 

 down as probable replicas of early spiders, and their webs are sig- 



