THE ARMATURE OF ORBWEBS : VISCID SPIRALS. 



87 



certainly made a mistake in saying that the suspensory lines are as often 

 studded with beads as the spirals.^ The radii are often found more or 

 less beaded, although this is a rather exce})tional and incidental condition ; 

 but I cannot recall, among the vast number of orlnvebs, a single instance 

 of beads upon the suspensory or foundation lines. The dewdrops gather 

 on those lines, however, and perhaps Ronnie, like some other observers, 

 was deceived by them. 



Under the microscope the beads show as beautiful objects, not unlike 

 pearls strung upon a cord. Indeed, were a jeweler to reproduce in exact 

 form and suitable magnitude a geometric web, substituting pearls 

 Beads ^'^^ beads, he would have a necklace of surpassing beauty. The 

 beads vary in size according to the size of the orb and its maker ; 

 they vary also upon the same orb and 

 line. Some have a thickness little greater 

 than the diameter of the line ; others are 

 several times greater, say in proportion of 

 6, 3, 4, and 2. The larger ones commonly 

 alternate with the smaller, two or more of 

 the latter succeeding the former, and this 

 sequence is tolerably constant, but it is by 

 no means absolute. Immediately after for- 

 mation the beads are uniform in size, and 

 the change in size is afterward caused prob- 

 ably by the interblending of two or more 

 of the original beads. (See Fig. 84.) 



They are for the most part semitrans- 

 parent or translucent. Frequently there 

 occur what appear to be opaque beads, 



showing quite black upon the line ; these are simply particles of dust, 

 around which a delicate coating of the spiral gum has gathered. Small 

 spherical objects, grains of pollen and the like, also are seen, and the orb 

 soon becomes well sprinkled over with minute extraneous particles, espe- 

 cially if the wind blows or the location is dusty. Under the microscoi)e 

 the beaded line shows through the substance of the globules, which is 

 evidently aggregated around it. Indeed, one may scrape oif the beads and 

 leave the line intact. Fig. 84 shows a few of these viscid beads as they 

 appear under a microscope. The sections I, II, III are from a snare of 

 Cyclosa caudata examined afield. Section IV is drawn from a snare of 

 Argiope argyraspis spun wliilc in confinement. It shows the beading 

 along a space of nearly five millimetres as marked off at a ; and also indi- 

 cated upon the magnified line. None of the beads upon this snare were 

 longer than about one-tenth of a iiiillinietre. In sliapc they were ovoid, 

 more or less pointed at the poles; many were globular and some liad 



Fir;. 84. Relative size and shapes of viscid 

 beads. The space beaded at IV is shoivn 

 at a, natural size. 



^ Insect Architocture, page 313. 



