The webs or nets of the different species of orb weavers differ in the details of their structure; but the general plan is quite similar. There is first a framework of supporting lines. The outer part of this framework is irregular, depending upon the position of the objects to which the net is attached; but the central part is very regular, and consists of a number of lines radiating from the center of the net (Fig. 91). All of these supporting lines are dry and inelastic. Touch them with your pencil and you find that they neither stretch nor adhere to it. Upon these radiating lines there is fastened in a very regular manner a thread which is sticky and elastic. This will adhere to your pencil, and will stretch several times its normal length before breaking. Usually this sticky thread is fastened to the radiating lines so as to form a spiral; but a few species make nets in which it is looped back and forth. And even in the nets where the greater part of the thread is in a spiral there are in most cases a few loops near the lower margin (Fig. 91). Examine the next orb-web you find and see whether it is true in that case. Many of the orb weavers strengthen their nets by spinning a zigzag ribbon across the center. This ribbon is made by spreading apart the spinnerets, the organs from which the silk is spun, and which will be described later. Ordinarily the tips of the spinnerets are held close together so that they form a single thread, but by spreading them apart many threads can be spun at once, thus forming a ribbon. Some orb weavers are not content with making a simple zigzag band across the center of the net, but weave an elaborate bit of lace in this position. Fig. 92 is from a photograph of the center of the net of one of these spiders, which was found near Ithaca. [Illustration: _Fig. 92. Lace-like hub of an orb-web._] In studying the various kinds of orb-webs one should pay particular attention to the center of the web; for this part differs greatly in the webs of the different species. There is usually a _hub_ composed entirely of dry and inelastic silk woven in an irregular manner; outside of this there are several turns of a spiral thread which is also dry; this constitutes the _notched zone_, a name suggested by the fact that the spiral line is attached for a short space to each radius it crosses, thus giving the line a notched course. In many cases it is here, on the hub and the notched zone, that the spider waits for its prey; and it is obvious that sticky silk in this place would be objectionable. Between the notched zone and the _spiral zone_, the part furnished with the sticky spiral thread, there is a clear space, the _free zone_, crossed only by the radii. This gives the spider an opportunity to pass from one side of the web to the other without going around the entire web.