1533. j AERONAUT SPIDEKS. 101 



from its spinners. These, glittering in tlie sunshine, might be 

 compared to diverging rays of light ; ihey were not, however, 

 straight, but in undulations like films of silk blown by the wind. 

 Thev were more than a yard in leng^th, and diver2:ed 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 afiect 

 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 net 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 tlie 

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

 that the habit of sailinof throuQ:h the air is as characterislic of 

 this tribe, as tiiat of diving- is of the Aro-vroneta. We m.av then 

 reject Latreille's supposition, that the gossamer owes its origin 

 indifferently to the young of several genera of spiders : althoi'.gl.', 

 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 caurrht many curious ani- 

 mals. Of Crustacea there were manv strange and undescribed 

 genera. One, which in some respects is allied to the IS^otopods 

 (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 penuhimate jonit, instead of terminating in a simple 

 claw, ends in three bristle-like appendages of dii^similar lengths — 



* Mr. Elackwall, in his Kescarches iu Zoology, has many cxcelieut ob- 

 servations on the habits of spiders. 



