Nets of Geometric Spiders. 187 



after her, and guiding it with one of her hind feet, till she reaches its 

 point of union with one of the adjoining radii : on to this radius she 

 steps, and passing along it to the other extremity, there makes fast her 

 thread; by this simple process connecting with marginal Hnes distant 

 objects between which no direct communication previously existed. 



In the formation of their nets Spiders are regulated chiefly by the 

 sense of touch, which they possess in high perfection. This is rendered 

 extremely probable by the general tenor of their proceedings ; for ex- 

 ample, they ascertain when they have the full complement of radii by 

 approaching the centre of the net, which is their common point of union, 

 and touching each in succession with the feet, supplying deficiencies 

 wherever they are perceived; and I have already remarked, which greatly 

 tends to confirm this opinion, that they generally construct their snares 

 in the night. The fact, however, is established beyond dispute by the fol- 

 lowing circumstance. I have repeatedly confined Spiders in glass jars 

 placed in situations absolutely impervious to light, and yet during their 

 captivity they have produced perfect nets of admirable workmanship. 



Spiders were supposed by Dr. Lister* to be able to retract tlieir 

 threads within the abdomen ; and whoever minutely observes the geome- 

 tricians when fabricating their silken snares, will be almost induced to 

 entertain the same belief. The viscid line produced in the Spider's 

 transit from one radius to another, is sometimes drawn out to a much 

 greater extent than is necessary to connect the two, yet on approaching 

 the point at which it is to be attached, it appears rapidJy to re-enter the 

 spinners, till it is reduced to the exact length required. This optical 

 illusion, for such it is, is occasioned by the extreme elasticity of the thread, 

 which may be extended several inches by the application of a sHght 

 force, and on its removal will contract into a minute globule of almost 

 inappreciable dimensions. The viscid line alone possesses this property 

 in a remarkable degree, (the radii and marginal lines being almost desti- 

 tute of it,) by which it is adapted to the frequent and rapid changes in 

 distance that take place among the radii when the net is agitated by winds 

 or other disturbing forces ; and by which the insects that fly against it 

 are more completely entangled than they otherwise could be, without 



* De Araneis, p. 8. 



