CONSTRUCTION OF AN OKBWKB. 



tendrils, frequently securing an anchorage by attaching her dragline, and 

 all the while holding aloof from contact with the foliage the new founda- 

 tion line which is spun after her as she moves. 



Kirby and Spence describe this curious variation of the habit. A spider 

 isolated upon a stick set within a vessel of water drop})ed from the top of 



the stick to which the usual dragline attachment had been made, 

 A Varia- .^j^j emitted two threads as it descended. Having reached a point 

 th H b't ^^^"'^^' ^'^® surface of the water, it stopped, and by some unobserved 



means, severed one of the threads close to the spinnerets. The 

 free end of the released filament floated up and outward from the top of 

 the stick, and was caused to entangle upon a pencil held in the observer's 

 hand. The spider, which had meanwhile mounted the summit of the stick, 

 perceived the line to be taut, and having tested it by pulling, crept over it to 

 the pencil, dragging another line behind her as she moved. ^ This is an iso- 

 lated example, and may, of course, have been a simple coincidence, as it is 

 not certain that the spider designed to secure a bridge line by the above 

 behavior. Yet it is worthy of notice as suggesting a line of observation 

 that may yield good results. 



II. 



We may now construct the diagramatic flgure. Fig. 67, to show tlie proc- 

 ess by which an orb frame is laid when the prime foundation is obtained 

 by an air current. We suppose that an Orbweaver in the act of web- 

 niaking has stopped upon the leaf at the left of the cut. Turning her 

 abdomen toward the course of the wind, she issues a line (a, a) that floats 

 outward until it entangles at x. This fact is at once perceived, and the 

 spider (ss) ventures over it as at bb, dragging behind her a thread which 

 unites with and strengthens the original line, which had been drawn taut, 

 as e, c, c, X. This may be repeated several times, until, at last, the prime 

 foundation line is formed. 



This strengthening by means of overspinning is not necessarily, perhaps 

 not generally, done in immediate succession of threads, but from time to time. 

 At various stages of working in the radii of other parts, the crea- 

 r^^^ ture seems to perceive the need of strengthening the supporting 



lines, and proceeds to stretch a new strand or two. Then she re- 

 sumes work upon the orb, to return as occasion reciuires, and adds strands 

 to her cable. When the upper line is completed, especially if it be one which 

 has been used for several days, it presents the appearance of a white or 

 yellowish white thread as thick as a bit of sewing silk. It may readily be 

 reeled upon a stick or spool, and its numerous filaments can be seen and 

 even separated. It has a glossy appeai-auce, and may often be found sev- 

 eral feet in length. 



1 Intro<Uiction to Entomology, Vuhiini' 1, set XIII., page 415. 



