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 Audes, 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. 1 n 
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 
antenn®, 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 severa 
hundred eggs. In going up one of the great rivers o 
America, it is observed, that the appearance of anew 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 Cano Tamalamec, 
is only perceived in the valley of the Rio Grande de 
Magdalena, at a league north of the junction of the tw° 
rivers ; it goes up, but scarcely ever descends the Ri° 
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 Culex pipiens of Europe does not, like the culex of the torrid 
zone, shun mountainous places. Giesecke suffered from these insects j 
Greenland, at Disco, in latitude 70°. They are found in Lapland » 
summer, a three or four hundred toises high, and at a temperature 
11° or 12°. 
