hoxo Spiders effect their aerial Excursions. 45.5 



comparatively still air of a room Avithout fire, both the lines and 

 webs descend slowly to the floor, the latter falling with the 

 greater deoree of velocity. 



Were these productions lighter than atmospheric air, or were 

 the spiders capable of effecting an ascent without the help of 

 adventitious aid, a calm though cloudy day might answer their 

 purpose ; but as considerable warmth is required to produce an 

 ascending current of rarefied air strong enough to bear them 

 from the earth, a bright as well as still day is indispensable. 



Founded on results obtained from an experiment which has 

 been frequently made, but never conducted with sufficient care, 

 is the belief entertained by many eminent entomologists that 

 spiders can forcibly propel or dart out threads from their papilhv. 

 Now as this process would, contrary to my own experience, im- 

 ply the exercise of a physical power peculiar to these creatures ; 

 and as attempts have been made to explain on this principle the 

 fabrication of their webs in situations where their ordinary mode 

 of proceeding could not be employed, I determined to repeat 

 the experiment from Avhich so strange a conclusion has been 

 deduced. With this view, having procured a small branched 

 twig, 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 Avere 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 mo- 

 tion of detached lines similarly exposed. The spiders, in the 



VOL. XV. 3 N next 



