1833.] AKRONAUT SPIDERS. 161 
from its spinners. These, glittering in the sunshine, might be 
compared to diverging rays of Hight; they were not, however, 
straight, but in undulations like films of silk blown by the wind. 
They. were more than a yard in length, and diverged in an ascend- 
ing direction from the orifices. The spider then suddenly let go 
its hold of the post, and was quickly borne out of sight. ‘The 
day was hot and apparently quite calm; yet under such circum- 
stances, the atmosphere can never be so tranquil as not to affect 
a vane so delicate as the thread of a spider’s web. If during a 
warm day we look either at the shadow of any, object cast on a 
bank, or over a level plain at a distant landmark, the effect of an 
ascending current of heated air is almost always evident: such 
upward currents, it has been remarked, are also shown by the 
ascent of soap-bubbles, which will not rise in an in-doors room. 
Hence I think there is not much difficulty in understanding the 
ascent of the fine lines projected from a spider’s spinners, and 
afterwards of the spider itself; the divergence of the lines has 
been attempted to be explained, I believe by Mr. Murray, by 
their similar electrical condition. ‘The circumstance of spiders 
of the same species, but of different sexes and ages, being found 
on several occasions at tite distance of many leagues from the 
land, attached in vast numbers to the lines, renders it probable 
that the habit of sailing through the air is as characteristic of 
this tribe, as that of diving is of the Argyroneta. We may then 
reject Latreille’s supposition, that the gossamer owes its origin 
indifferently to the young of several genera of spiders: although, 
as we have seen, the young of other spiders do possess the power 
of performing aérial voyages.* 
During our different passages south of the Plata, I often towed 
astern a net made of bunting, and thus caught many curious ani- 
mals. Of Crustacea there were many strange and undescribed 
genera. One, which in some respects is allied to the Notopods 
(or those crabs which have their posterior legs placed almost on 
their Backs, for the purpose of adhering to the under side of 
rocks), is very remarkable from the structure of its hind pair of 
legs. The penultimate joint, instead of terminating in a simple 
claw, ends in three bristle-like appendages of dissimilar lengths— 
* Mr. Blackwall, in his Researches in Zoology, has many excellent ob- 
servations on the habits of spiders. 
