SHEET-BUILDING SPIDERS 153 



taneous effect. For when an insect becomes entangled 

 in a snare and is struggling to escape, it forcibly exerts 

 its legs and wings in the attempt to tear itself away. 

 By the force of these violent efforts it often does escape, 

 and on all occasions injures the snare. The move- 

 ments of the legs and wings cause the greatest damage, 

 so it is necessary that the spider should quickly subdue 

 these and render its prey helpless. The movements 

 of these parts are under the control of a nervous 

 ganglion situated in the insect's thorax, and the spider 

 acts as though it were well aware of this fact. It 

 behaves as though it understood that the thorax is the 

 vital spot and that into the substance of this part it 

 must strike. On every occasion on which I have 

 observed the spider seize its prey it has struck un- 

 hesitatingly straight into the thoracic ganglion, pro- 

 ducing an immediate paralysis of the legs and wings. 

 It behaves with a similar skill to the tarantula of 

 M. Fabre, that struck into the one vital point in the 

 whole nervous chain. Wonderful as are the instincts 

 of the geometrical spiders in the weaving of their 

 beautiful snares, no less fascinating are the instincts of 

 this humbler species in the exactness of its knowledge 

 of the vital anatomical point and the perfect precision 

 of its stroke. 



I think it is a matter of some doubt among natural- 

 ists whether or not the smaller species of spiders 

 actually inject poison into their insect prey. I am 

 inclined to believe that they do. For an insect, after 

 being seized by the Hippasa, is paralyzed in an 

 extremely short space of time, far shorter than could 

 result from mere penetration of the thorax. The legs 

 and wings are in an instant struck motionless. If the 



