1881.] 



NATURAL SCIENCES OF PHILADELPHIA. 



165 



The orb ma}' be said to be composed of a series of independent 

 rays or sectors, each ray composed of several spirall}' crossed 

 radii, and the whole series united into an orl) by cross-lines or 

 spirals like those which unite the radii. In the shifting of the 

 section-lines above referred to, this separation of the orb into in- 

 dependent rays, is always quite evident. The spirals are covered 

 with viscid beads, as in most orb-webs The radii do not all 

 pass to the Hub or Centre, as do those of orb-webs generally, but 

 converge for the most part upon the axes of the rays as repre- 

 sented at figs. 1, 2, 3. These axes themselves converge upon a 



Fig. 5.— View from front. "Web taut. Perspective not t^liown . Central opening exact. 



single strong thread, a trap-line, T ( figs. 1 and 2, and succeeding 

 cuts), which is attached to some part of the surrounding surface, 

 of rock, earth or plant. When the snare is flat or relaxed, as was 

 the case with the one drawn at fig. 2, and as appears in fig. 1, the 

 trap-line is often about perpendicular to the plane of the orb, as is 

 the handle to the Ta.ys of an open Japanese umbrella. This, how- 

 ever, depends somewhat upon the environment ; a convenient 

 point for the attachment of the trap-line will cause the animal to 

 divert the thread more or less from the perpendicular. 



