1833.] AERONAUT SPIDERS. 150 



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 ap- 

 parently quite calm; yet under such circumstances, the atmo- 

 sphere 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 diificulty 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 ex- 

 plained, I believe by Mr. Murray, by their similar electrical con- 

 dition. 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 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 aerial voyages.* 



During our different passages south of the Plata, I often towed 

 astern a net made of bunting, and thus caught many curious 

 animals. 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 

 the longest equalling that of the entire leg. These claws are very 



* Mr. Blackwall, in his Researches in Zoology, has many excellent 

 observations on the habits of spielers. 



