96 



appear. At fixed and invariable hours, in the 

 same season, and the same latitude, the air is 

 peopled with new inhabitants, and in a zone 

 where the barometer becomes a clock*, where 

 every thing proceeds with such admirable regu- 

 larity, we might guess blindfold the hour of the 

 day or night, by the hum of the insects, and by 

 their stings, the pain of which differs according to 

 the nature of the poison, that each insect depo- 

 sits in the wound. 



At a period when the geography of animals-* 

 and of plants had not yet been studied, the 

 analogous species of different climates were often 

 confounded. It was believed, that the pines 

 and ranunculuses, the stags, the rats, and the 

 tipulary. insects of the north of Europe, were to 

 be found in Japan, on the ridge of the Andes, 

 and at the straits of Magellan. Naturalists 

 justly celebrated have thought, that the zancudo 

 of the torrid zone was the gnat of our marshes, 

 become more vigorous, more voracious, and 

 more noxious, under the influence of a burning 

 climate. This is a very erroneous opinion. I 

 carefully examined and described upon the spot 

 those zancudoes, which torment us the most. 

 In the rivers Magdalena and Guayaquil alone 

 there are five distinct species. Mr. La- 



* By the extreme regularity of the horary variations of 

 the atmospheric pressure. 



