232 



nets in wliicli 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. 115). Examine the 

 next orb-web you will find and see if 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 tiie 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 form- 

 ing a ribbon. 



Some orb weavers are not content with making a simple zigzag 

 band across the center of the net, but w^eave an elaborate bit of 



lace in this position. Figure 116 is from a photo- 

 graph of the center of the net of one of these 

 spiders, which w^as found near Ithaca. 



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 huh com- 



116. — Lace-likehub i .• i ^ i i i -• -n ' 



, , posed entn-ely oi dry and elastic silk woven m an 

 of ail oro-weo. ^ j j 



irregular manner ; outside of this there are several 

 tnrns 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 obvi- 

 ous 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, tlie free zone, crossed 

 only l)y 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. 



Some orb weavers do not wait upon the hub, but have a retreat 

 near one edge of the net, in wdiich they hang back downwards. 

 While resting in these retreats they keep hold of some of the lines 



332 



