THE AERONAUTIC OR BALLOONING HABIT. 



261 



cleared away, and during ascent upon a dropped dragline after a spider has 

 thrown herself from her snare. But it became especially interesting at that 



moment, for at once it suggested an act of volition on the part 

 Control- o tjjg Lycosid, by which, in a measure at least, it might control 

 * ng its descent. Evidently the shortening of the overhanging thread 



operated like the furling of sails upon a vessel, and decreasing the 

 motion of the spider increased the influence of gravity upon the body, 

 which thus sank toward the ground. At the same time, the diminution of 

 the surface of the thread above, and the increase of bulk at the mouth 

 (trifling as it might be), tended to increase the buoyancy of the whole, and 

 allowed the creature to fall. The same effect was thus produced by the 

 spider aeronaut, and by a strikingly analogous mode, as that which the 

 human aeronaut accomplishes when he con- 

 tracts the surface of his balloon by causing 

 the inflating gas to escape. 



The manner in which the lines of spi- 

 ders are carried out from the spinnerets by 

 ' a current of air appears to be 



How Fila ~ thus : As a preparatory measure, 

 ments are ,, i i , , 



T-, .,, , the spinnerets are brought into 

 Emitted. & . 



close contact, and the liquid silk 



is emitted from the spinning tubes; the 

 spinnerets are then separated by a lateral 

 motion, which breaks up the silk into fine 

 filaments; on these filaments the air current 

 impinges, drawing them out to a length 

 which is regulated by the will of the ani- 

 mal; and, on the spinnerets being again 

 brought together, the filaments coalesce and 

 form a compound line. 1 According to Mr. 

 Emerton, 2 the line seems to come from the middle pair of spinnerets 

 only, but the posterior pair were In constant motion, folding together 

 over the middle ones and then spreading apart as if to help throw out 

 the threads. 



FIG. 273. FIG. 274. 



FIG. 273. Floating with head depressed, 

 holding to a foot basket. FIG. 274. Bal- 

 looning spider gathering in its threads 

 for descent. 



III. 



It will here be in place, and will add to the understanding of the 

 reader, to insert a few field notes giving in detail the above and some 

 further facts as to the posture and action of spiders before and during 

 flight. 



1 "Blackwall on the Structure, Functions, and Economy of the Araneidea," Ann. and 

 Mag. of Nat. Hist., Vol. XV., page 241, 1845. 



2 " Flying Spiders," American Naturalist, 1872, page 168. 



