1912] Evolution of the Webs of Spiders 9 
is built the hub of the web, the nature of which varies greatly 
in the webs of different divisions of the family. Extending 
from the hub a spiral line is spun upon the radii the turns of 
which are a considerable distance apart. As the function of 
this line is merely to hold the radii in place during the later 
stages of the web building, I have designated it the spiral guy 
line. This, like all portions of the web made up to this point is 
composed of dry silk. After the radii have been firmly stayed 
by the spiral guy line, the spider beginning at the outer edge of 
the orb and adds the loops and turns of the viscid line, destroy- 
ing the spiral guy line as it progresses. 
Frequently the remains of the spiral guy line can be seen as 
a series of regularly spaced dots on the radii of completed webs. 
Great differences exist in the different webs of orb-weavers 
as to the relative amount of dry and viscid silk, one extreme 
is illustrated by the web of Metepeira; the other, by the web 
of Cyclosa. 
In the webs of most orb-weavers, the entire orb is replaced 
frequently, only the outer foundation lines being a permanent 
investment. The spiral guy line is destroyed during the build- 
ing of the web, the radii and viscid line are sacrificed when it is 
necessary to renew the orb. 
But in the webs of Nephila we find that the web is so con- 
structed that it is only necessary to renew the viscid line as it 
becomes injured or dry. . 
Here is attained the extreme of economy in the use of the 
dry silk, although the first investment is somewhat greater 
than in ordinary orb-webs. The orbicular part of an ordinary 
-orb-web may be compared to a shack built for a day; the orb 
of Nephila, to a permanent structure built to stand during the 
life time of the occupant. 
This difference is brought about by radical differences in 
‘the style of architecture. In the orb of Nephila the radii are 
forked, which results in the outer part of the orb being as firm 
-as the central portion. The spiral guy line is attached to each 
radius lengthwise for a short distance; as this guy line is pulled 
taut it draws the radius out of its direct course; the course of 
-each radius is, therefore, zigzag. The viscid line is looped 
back and forth between the turns of the guy line, and gives the 
-web a banded appearance. When the web is repaired only the 
