MOTIONS OF INSECTS. 339 



ihg, 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 

 I'ise increases. I have myself more than once observed 

 these creatures take their flight, and find the following 

 niemoranduni with respect to their mode of proceeding. 

 *' The spider first extends its thigh, shank, and foot 

 into a right line, and tlien elevating its abdomen till it 

 becomes vertical, shoots its tliread into the air, and flies 

 off from its station." It is not often, however, that an 

 ©bserver can be gratified Avith this interesting sight, 

 since these animals are soon alarmed. I have frequently 

 noticed them — for at the times when tliese webs are float- 

 ing in the air they are very numerous — on the vertical 

 angle of a post, or pale, or one of the uprights of a gate, 

 with the end of their abdomen pointing upwards, as if to 

 shoot their thread previously to flying off; when, upon 

 my approaching to take a nearer view, they have low- 

 ered it again, and persisted in disappointing my wish 

 to see them mount aloft. The rapidity with which the 

 spider vanishes from the sight upon this occasion and 

 darts into the air, is a problem of no easy solution. Caij 

 the length of web that they dart forth counterpoise the 

 weight of their bodies ? Or have they any organ analo- 

 gous to the natatory vesicles of fishes % which contri- 

 butes at their will to render them buoyant in the air ? 

 Or do they rapidly ascend their threads in their usual 

 way, and gather them up, till having collected them 

 into a mass of sufficient magnitude, they give themselves 

 to the air, and are carried here and there in these cha- 

 riots ? 1 must here give you Mr. White's very curious 



" Cuvicr, Jnnt. Coiup, i. 501, 

 Z 2 



