V] OF SPIDEKS' WEBS 385 



slacker cross-threads as they issue to form the spiral portion of the 

 web. This latter secretion is more fluid than the first, and only 

 dries up after several hours*. By capillarity it "wets" the thread, 

 spreading over it in an even film or liquid cylinder. As such it 

 has its limits of stabihty, and tends to disrupt at points more 

 distant than the theoretical wave-length, owing to the imperfect 

 fluidity of the viscous film and still more to the frictional drag of 

 the inner thread with which it is in contact. Save for this qualifi- 

 cation the cyhnder disrupts in the usual manner, passing first into 

 the wavy outhne of an unduloid, whose swollen internodes swell 

 more and more till the necks between them break asunder, and leave 

 a row of spherical drops or beads strung like dewdrops at regular 

 intervals along the thread. If we try to varnish a thin taut wire 

 we produce automatically the same identical result t; imless our 

 varnish be such as to dry almost instantaneously it gathers into 

 beads, and do what we will we fail to spread it smooth. It follows 

 that, according to the drying quahties of our varnish, the process 

 may stop at any point short of the formation of perfect spherules; 

 and as our final stage we may only obtain half-formed beads or the 

 wavy outlines of an unduloid. The beads may be helped to form 

 by jerking the stretched thread, and so disturbing the unstable 

 equilibrium of the viscid cyhnder. This the spider has been said 

 to do, but Dr G. T. Bennett assures me that she does nothing of the 

 kind. She only draws her thread out a little, and leaves it a trifle 

 slack ; if the gum should break into droplets, well, and good, but it 

 matters httle. The web with its sticky threads is not improved 

 thereby. Another curious phenomenon here presents itself. 



In Plateau's experimental separation of a cyhnder of oil into two 

 spherical halves, it was noticed that, when contact was nearly 

 broken, that is to say when the narrow neck of the unduloid had 

 become very thin, the two spherical bullae, instead of absorbing 

 the fluid out of the narrow neck into themselves as they had done 

 with the preceding portion, drew out this small remaining part of 



* When we see a web bespangled with dew of a morning, the dewdrops are not 

 drops of pure water, but of water mixed with the sticky, gummy fluid of the cross- 

 threads ; the radii seldom if ever shew dewdrops. See F, Strehlke, Beobachtungen 

 an Spinnengewebe, Poggendorff's Annalen, XL, p. 146, 1937. 



t Felix Plateau recommends the use of a weighted thread or plumb-line, to be 

 drawn up slowly out of a jar of water or oil; Phil. Mag. xxxiv, p. 246, 1867. 



