108 Transactions. — Zoology. 



then they both ran away in opposite directions, the bridge 

 having been broken in the melee. Shortly after the medium- 

 sized spider had estabhshed a bridge between the two sticks, 

 at about half their height. I presume this was done in the 

 same way as the first longer bridge ; this one was about 2^m. 

 long. He then went to the top of one stick, attached a line 

 there, ran down, crossed the bridge, and carried the line to 

 the top of the other stick, tightened it in and secured it — just 

 as a sailor would have hauled taut and belayed. Then he 

 crossed this upper bridge, strengthening it by an additional 

 line which he spun out as he went. The large spider then 

 crossed the upper bridge, spinning out his own line as he went. 

 Then the two spiders started to cross this bridge from the 

 opposite ends, met in the middle, sparred with one another, 

 and both retired. 



These observations seem to show that the geometric spiders 

 do not see, or see very imperfectly, but that they have the 

 instinct to throw out a line when they find themselves on an 

 isolated elevation ; that they are very sensitive to draughts of 

 air, and always lay out line to leeward. Apparently they 

 trust to their good-fortune, when the line is floated out, that 

 it may catch on something, and they are sensitive to the 

 feeling of the line when it does catch. The hauling on the 

 line to see if it is firmly enough attached to bear the 

 creature's weight seems almost like reason, as does also 

 the mode of forming a higher bridge by means of a lower 

 one. 



The fact that these spiders can walk on the bottom of a 

 pool of water in case of need is remarkable, as it gives them 

 another means of crossing narrow pieces of water. The 

 spider could not walk on the smooth surface of the pan of 

 water, but ran nimbly on the potato ; so that a rough surface, 

 to which it can cling, seems needful for the feat. Probably it 

 carries a bubble of air down with it, and so can live for a time 

 under water, and float up again before the air is exhausted. 



