278 EUROPEAN AND TROPICAL VARIETIES. 



the pain of which differs according to the nature of the 

 poison that each species deposits 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. 

 Justly celebrated naturalists 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 in- 

 fluence of a burning climate. This is a very erroneous 

 opinion. I carefully examined and described upon the spot 

 those zancudos, the stings of which are most tormenting. In 

 the rivers Magdalena and Guayaquil alone there are five dis- 

 tinct species. 



The culices of South America have generally the wings, 

 corslet, and legs of an azure colour, ringed and variegated 

 with a mixture of spots of metallic lustre. Here as in 

 Europe, the males, which are distinguished by their feathered 

 antenna, are extremely rare ; you are seldom stung except 

 by females. The preponderance of this sex explains the 

 immense increase of the species, each female laying several 

 hundred eggs. In going up one of the great rivers of 

 America, it is observed, that the appearance of a new species 

 of culex denotes the proximity of a new stream flowing in. 

 I shall mention an instance of this curious phenomenon. 

 The Culex lineatus, which belongs to the Cafio Tamalamec, 

 is only perceived in the valley of the Hio Grande de la 

 Magdalena, at a league north of the junction of the two 

 rivers; it goes up, but scarcely ever descends the Rio 

 Grande. It is thus, that, on a principal vein, the appearance 

 of a new substance in the gangue indicates to the miner the 

 neighbourhood of a secondary vein that joins the first. 



On recapitulating the observations here recorded, we see, 

 that within the tropics, the mosquitos and zancudos do not 

 rise on the slope of the Cordilleras* toward the temperate 



* The yulex pipiens of Europe does not, like the culex of the torrid 

 zone, shun mountainous places. Giesecke suffered from these insects in 

 Greenland, at Disco, in latitude 70. They are found in Lapland in 

 summer, a three or four hundred toises high, and at a temperature of 



