280 ON THE NETS OF GEOMETRIC SPIDERS. 
and exterior threads remain unsoiled. These viscid 
threads mainly serve to retain the insects which fly 
into the net; and as they lose their adhesive property 
by exposure to the air, it is requisite that they 
should be- frequently renewed—a process not ne- 
glected by the spider, which evinces a perfect con- 
sciousness of its necessity. Placing herself at the 
circumference of the net, and fastening her viscid 
thread to the end of one of the radii, the spider 
walks up that radius towards the centre, till she 
comes in contact with the last produced circumvo- 
lution of the unadhesive spiral line, along which 
she passes to the adjoining radius, drawing out the 
thread, in her transit, with the claws of the hind 
leg nearest to the circumference. She then transfers 
the thread to the claws of the other hind leg, and 
passing down the radius at which she has just 
arrived towards the circumference she places the 
foot of the hind leg previously employed in drawing 
out the thread on that pomt in the radius to which 
her filament is to be attached, and, bringing the 
spinners to the spot, there makes it secure. The 
precise place im each radius at which to fix the 
thread is always ascertained by the situation of the 
foot of the hind leg; and this is determined by 
touching, with the feet of those legs nearest to the 
circumference, the marginal line, or, when the struc- 
ture of the net is further advanced, the last-formed 
circumvolution of the viscid spiral line. As this last 
