THE CRIBELLATE SPIDERS 153 



ing grounds to the point of attachment and then pulling the line 

 tight; but in many instances air currents are called upon to balloon 

 the line to a mooring point, as is the practice of the typical orb 

 weavers. A vertical thread from one end of the bridge line is tied 

 to a twig, and forms the arc of the sector. The third principal line 

 returns to near the other end of the bridge line and completes the 

 triangle. Then, between the radial lines, Hyptiotes places two more 

 rays. 



At this stage the spider has constructed a sector of four rays 

 attached at one end to a single line and at the other to an arc thread. 

 Upon this must now be placed the viscid threads that will make the 

 web a trap. But before the sticky lines are added, Hyptiotes spins 

 a row of three or four dry scaffolding threads, extending from the 

 apex toward the middle of the triangle, that serve to steady the 

 web by holding the radii in place, and that will simplify the laying 

 down of the cribellar silk by providing a bridge from ray to ray. 

 These scaffolding threads are analogous to the dry spirals or spiral 

 bridge of the ecribellate orb weavers, are put down in the same 

 sequence from the apex of the triangle (or hub) outward, and are 

 eliminated in much the same way bitten out when the web is fin- 

 ished. 



To lay down the viscid sections, Hyptiotes crawls along the up- 

 permost ray nearly to the point at which it joins the arc line, spins 

 and attaches a band of sticky silk, then crawls back toward the 

 middle of the triangle, spinning as she goes and holding the thread 

 free of the ray. When she reaches the outermost scaffolding thread, 

 she descends upon it to the ray immediately below, and upon this 

 returns, reeling the sticky line back in, until she is immediately be- 

 low the first point of attachment. Here she fixes her line. In 

 order to put down this first vertical cribellar thread, which extends 

 only three inches or so between the two upper rays, Hyptiotes must 

 often crawl forward and backward a dozen inches. One might ask 

 at this point why Hyptiotes does not drop down directly to the 

 ray below? The triangle spider knows her web only by the touch 

 of the silk, cannot see or know the position of the other rays, and 

 is dominated by instinctive actions that keep her pursuing a pre- 

 scribed course. 



The spider continues this roundabout process until the four rays 

 are bound together by a slightly zigzag vertical line of three sec- 

 tions. She then crawls around the triangle to the top ray once 

 more, and starts on a second line, using her legs to measure its dis- 



