The Life of Spiders 



In the webs of some spiders the viscid thread extends in but 

 few if any spiral turns; the great part of thread being looped back 

 and forth on the radii. This is well-shown in the web of Nepbila 

 (Fig. 439) and in that of Metepeira labyrinthea (Fig. 187). Such 

 a web is termed an incomplete orb. 



In an ordinary incomplete orb there is a lack of regularity 

 in the position of the turns of the viscid thread, different loops 

 ending on different radii. But the species of Zilla and certain 

 species of Aranea sometimes 

 make an incomplete orb in 

 which the viscid line is omit- 

 ted from a definite sector of 

 the orb (Fig. 470). As this 

 type of web is more often 

 made by the species of Zilla 

 than by other spiders, 1 sug- 

 gest that it be designated as 

 the {ilia type of orb-web. 



In the zilla type of web 

 there is a trapline extending 

 from the hub to a retreat 

 above the web; this trapline 

 is opposite the vacant sector 

 of the web. 



The making of a zilla type 

 of web is not even a specific 

 characteristic. 1 have had a 

 spider under observation in our 

 insectary make a complete orb 

 one day and replace it the next 

 day by one of the zilla type. 



A single known species, Hen{fia basilica, makes, according 

 lo the observations of Dr. McCook ('89 I. 164), a complete orb 

 and then pulls it into a dome-shaped structure. Such a web is 

 termed a domed orb. 



The web of Theridiosoma gemmosum (Fig. 415) differs from 

 other orb-webs in lacking a definite centre or hub, the radii being 

 grouped into several irregular groups or rays. This web was 

 named by Dr. McCook a ray-formed orb-web. 



The web of Lloborus (Fig. 239) is a complete orb, but it 



FiR. tS 7 . 

 WEB OF METEPEIRA LABYRINTHEA 



•95 



