188 



RIO PLATA. 



Dec. 1833. 



has been observed by Strack : may it not be in consequence 

 of the little insect having passed through a dry and rarefied 

 atmosphere ? Its stock of web seemed inexhaustible. While 

 watching some that were suspended by a single thready 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 in a lateral course, 

 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 

 is 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 glit- 

 tering in the sunshine, might be compared to rays of 

 light ; they were not, however, straight, but in undulations 

 like a film 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, 

 and was quickly borne out of sight. The day was hot and ap- 

 parently quite calm ; yet under such circumstances the atmos- 

 phere 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 will almost always be evident. And this 

 probably would be sufficient to carry with it so light an object 

 as the little spider on its thread. 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 



