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 lines 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 their 
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 rapidly 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 slight 
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. 
