i66 SPIDERS. [chap. viii. 



at the shadow of any object cast on a bank, or over a 

 level plain at a distant landmark, the effect of an ascend- 

 ing 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 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 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 m three bristle-like appendages of dis- 

 similar lengths — the longest equalling that of the entire 

 leg. These claws are very thin, and are serrated with 

 the finest teeth, directed backwards ; their curved extrem- 

 ities are flattened, and on this part five most minute 

 cups are placed which seem to act in the same manner 

 as the suckers on the arms of the cuttle-fish. As the 

 animal lives in the open sea, and probably wants a place of 

 rest, I suppose this beautiful and most anomalous structure 

 is adapted to take hold of floating marine animals. 



In deep water, far from the land, the number of living 

 creatures is extremely small : south of the latitude 35°, 



* Mr. Blackwall, in his "Researches in Zoologry," has many excellent 

 observations on the habits of spiders. 



