128 SHOOTING SPIDERS' LINES. 



more ambitious purpose of bearing Mm upwards when dis- 

 posed to mount in air. 



Conjectures, numerous and intricate as these aeronautic 

 threads, and often baseless as themselves, when detached from 

 their point d'appui, have been hazarded on the above curious 

 subject ; but it seems now pretty clearly ascertained,* that air 

 is the chief and indispensable agent in the shooting of the lines, 

 and consequent progress or ascent of the aeronautic spider. 

 Several of these insects were placed on a branch fixed upright 

 in a vessel of water. On exposure to a slight current of air, 

 they all directed their chests towards the quarter from whence 

 it came, and each emitted, from its raised spinneret, a small 

 portion of glutinous matter which was instantly carried out 

 into a line. The Spiders then ascertained by pulling at them 

 with their legs, whether or not these threads had taken hold 

 of, and become attached to. any object, and in this case, after 

 having tightened, they made them fast to the branch they 

 occupied, thus forming bridges for escape over which they 

 passed in safety, drawing after them a second line as a security 

 in case the first should fail. This was always their mode of 

 proceeding when in the way of a current ; but under a bell- 

 glass some were found to remain seventeen days without being 

 able to produce a single line, whereby to quit their water-girt 

 branch of durance. By a thread similarly produced, but un- 



* See experiments of Mr. Black-wall in Phil. Trans. Also of Mr. Eennie, Ins. 

 Architecture, p. 339. 



