-288 ON THE NETS OF GEOMETRIC SPIDERS. 
whoever minutely observes the geometricians when 
fabricating their silken snares will be almost in- 
duced 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 at- 
tached, it appears rapidly to reenter 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 ex- 
tended greatly by the application of a shght force, 
and, on its removal, will contract proportionally. 
The viscid line alone possesses this property in an 
extraordinary degree (the radii and marginal lines 
being scarcely remarkable for 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 doing extensive injury to the framework 
of the snare. 
In order to determine whether objects entangled 
in their toils are animate or inanimate, the Geometric 
Spiders pull with their feet the radii immediately 
in connexion with that part of the snare in which 
they are suspended, and, suddenly letting go their 
hold, produce by these means a vibratory motion 
