376 Insect Architecture. 



Mr. Black wall, "I fixed it upright in an earthen vessel 

 containing water, its base being immersed in the liquid, 

 and upon it I placed several of the spiders which produce 

 gossamer. Whenever the insects thus circumstanced were 

 exposed to a current of air, either naturally or artificially 

 produced, they directly turned the thorax towards the 

 quarter whence it came, even when it was so slight as 

 scarcely to be perceptible, and elevating the abdomen, they 

 emitted from their spinners a small portion of glutinous 

 matter, which was instantly carried out in a line, consisting 

 of four finer ones, with a velocity equal, or nearly so, to 

 that with which the air moved, as was apparent from 

 observations made on the motion of detached lines similarly 

 exposed. The spiders, in the next place, carefully ascer- 

 tained whether their lines had become firmly attached to 

 any object or not, by pulling at them with the first pair of 

 legs; and if the result was satisfactory, after tightening 

 them sufficiently, they made them pass to the twig; then 

 discharging from their spinners, which they applied to the 

 spot where they stood, a little more of their liquid gum, 

 and committing themselves to these bridges of their own 

 constructing, they passed over them in safety, drawing a 

 second line after them, as a security in case the first gave 

 way, and so effected their escape. 



"Such was invariably the result when spiders were 

 placed where the air was liable to be sensibly agitated : I 

 resolved, therefore, to put a bell-glass over them ; and in 

 this situation they remained seventeen days, evidently 

 unable to produce a single line by which they could quit the 

 branch they occupied, without encountering the water at 

 its base ; though, on the removal of the glass, they regained 

 their liberty with as much celerity as in the instances 

 already recorded. 



"This experiment, which, from want of due precaution, 

 has misled so many distinguished naturalists, I have tried 

 with several geometric spiders, and always with the same 

 success."* 



* Linn. Trans., vol. xv. p. 456. 



