MOTIONS OF INSECTS. 335 



take their flight, and find the following memorandum 

 with respect to their mode of proceeding. " The spi- 

 der first extends its thighs, shanks, and feet, into a right 

 line, and then elevating its abdomen till it becomes verti- 

 cal, shoots its thread into the air, and flies off from its sta- 

 tion." It is not often, however, that an observer can be 

 gratified with this interesting sight, since these animals 

 are soon alarmed. I have frequently noticed them for 

 at the times when these webs are floating 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 ap- 

 proaching to take a nearer view, they have lowered 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. Can the length 

 of web that they dart forth counterpoise the weight of 

 their bodies ; or have they any organ analogous to 

 the natatory vesicles of fishes % which contributes at their 

 will to render them buoyant in the air ? Or do they ra- 

 pidly ascend their threads in their usual way, and gather 

 them up, till having collected them into a mass of suffi- 

 cient magnitude, they give themselves to the air, and 

 are carried here and there in these chariots ? I must 

 here give you Mr. White's very curious account of a 

 shower of these webs that he witnessed. On the 21st 

 of September 1741, intent upon field diversions, he rose 

 before day-break ; but on going out, he found the whole 

 face of the country covered with a thick coat of cobweb, 

 * Cuvier, Anat. Comp. i. 504. 



