183:i.J AERONAUT SPIDERS. Kil 



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 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 th« 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 the distance of many leagues from the 

 land, attached in vast numbers to the lines, renders it probable 

 that the habit of sailino: throu2:h 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 : althoiigli, 

 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 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. Blackball, in his Researches in Zoology, ha.s many excellent ob- 

 servations on the habits of spiders. 



