MOTIONS OF INSECTS. 339 
have myself more than once observed these creatures 
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—tfor 
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 
* Cuvier, Anat. Comp. i. 504. 
Z 2 
