170 
RIO PLATA 
CHAP. 
watching some that were suspended by a single thread, I 
several times observed that the slightest breath of air bore them 
away out of sight, in a horizontal line. On another occasion 
(25th) under similar circumstances, I repeatedly observed the 
same kind of small spider, either when placed or having crawled 
on some little eminence, elevate its abdomen, send forth a thread, 
and then sail away horizontally, but with a rapidity which was 
quite unaccountable. I thought I could perceive that the spider, 
before performing the above preparatory steps, connected its 
legs together with the most delicate threads, but I am not sure 
whether this observation was correct. 
One day, at St. Fe, I had a better opportunity of observing 
some similar facts. A spider which was about three-tenths 
of an inch in length, and which in its general appearance 
resembled a Citigrade (therefore quite different from the 
gossamer), while standing on the summit of a post, darted 
forth four or five threads from its spinners. These, glittering 
in the sunshine, might be compared to diverging rays of light ; 
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 ascending 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 circumstances, 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 indoors room. Hence I 
think there is not much difficulty in understanding the ascent 
of the fine lines projected from a spider’s spinners, and after¬ 
wards 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 the 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 
