XIV ORB-WEBS 345 
As has been said, the spider can throw into play a varying 
number of spinning tubes at will, and in point of fact those 
used in laying down these foundation-lines are either two or 
four in number. The spider, however, often finds it necessary to 
strengthen such a line by going over it afresh. 
Every one must have noticed that orb-webs frequently bridge 
over gulfs that are clearly quite impassable to the spider in the 
ordinary way. They often span streams—and Epeirid spiders 
cannot swim—or they are stretched between objects unattainable 
from each other on foot except by a very long and roundabout 
journey. When tiis is the case, the animal has had recourse to 
the aid of the wind. A spider of this family placed on a stick 
standing upright in a vessel of water is helpless to escape if the 
experiment be tried in a room free from draughts. With air- 
currents to aid it, silken streamers will at length find their way 
across the water and become accidentally entangled in some 
neighbouring object. When this has happened, the spider hauls 
the new line taut, and tests its streneth by gently pulling at it, 
and if the result is satisfactory, it proceeds to walk across, hand- 
over-hand, in an inverted. position, carrying with it a second line 
to strenethen the first. This is exactly what happens in nature 
when a snare is constructed across chasms otherwise impassable, 
and it may be imagined that the spider regards as very valuable 
landed property the foundation lines of such a web, for, if de- 
stroyed, the direction or absence of the wind might prevent their 
renewal for days. They are accordingly made strong by repeated 
journeys, and are used as the framework of successive snares, till 
accident at length destroys them. 
A single line which finds anchorage in this way is sufficient 
for the purposes of the spider. It has only to cross over to the 
new object, attach a thread to some other point of it, and carry 
it back across the bridge to fix it at a convenient spot on the 
surface which formed the base of its operations. Between two 
such bridge-lines the circular snare is constructed in a manner to 
be presently described. Sometimes the tentative threads emitted 
by the spider travel far before finding attachment. In the case 
of the Enelish Epeira diademata the writer has measured bridge- 
lines of eleven feet in length; and with the great Orb-weavers of 
tropical countries they frequently span streams several yards in 
width. 
