272 



MOTIONS OF INSECTS. 



finger, if you take them into your hand. Last summer one 

 alighted on my book as I was reading in the parlour ; and 

 running to the top of the page and shooting out a web, took 

 its departure from thence. But what I most wondered at 

 was, that it went off with considerable velocity in a place 

 where no air was stirring; and I am sure that I did not 

 assist it with my breath. So that these little crawlers seem 

 to have while mounting some locomotive power without the 

 use of wings, and move faster than the air in the air itself." 1 

 A writer in the last number of Thomson's Annals of Phi- 

 losophy* 1 , under the signature of Carolan, has given some 

 curious observations on the mode in which some geometric 

 spiders shoot and direct their threads, and fly upon them ; 

 by which it appears that as they dart them out they guide 

 them as if by magic, emitting at the same time a stream of 

 air, as he supposes, or possibly some subtile electric fluid. 

 One, which was running upon his hand, dropped by its thread 

 about six inches from the point of his finger, when it im- 

 mediately emitted a pretty long line at a right angle with 

 that by which it was suspended. This thread, though at first 

 horizontal, quickly rose upwards, carrying the spider along 

 with it. When it had ascended as far above his finger as it 

 had dropped before below it, it let out the thread by which it 

 had been attached to it, and continued flying smoothly up- 

 wards till it nearly reached the roof of the room, when it 

 veered on one side and alighted on the wall. In flying, its 

 motion was smoother and quicker than when a spider runs 

 along its thread. He observes, that as the line lengthens 

 behind them, the tendency of spiders to rise increases. I 

 have myself more than once observed these creatures take 

 their flight, and find the following memorandum with respect 

 to their mode of proceeding: — " The spider first extends its 

 thighs, shanks, and feet into a right line, and then elevating 

 its abdomen till it becomes vertical, shoots its thread into the 

 air, and flies off from its station." It is not often, however, 

 that an observer can be gratified with this interesting sight, 

 since these animals are soon alarmed. I have frequently 



i Nat. Hist. I 327. 



2 No, lii. 306. 



