95 



a swelling that remains several weeks. It's 

 hum resembles that of our gnats in Europe, but 

 is louder and more prolonged. The Indians 

 pretend to distinguish " by their song" the zan- 

 cudoes and the tempraneroes ; the latter of 

 which are real twilight insects, while the zancu- 

 does are most frequently nocturnal insects, and 

 disappear toward sunrise. 



In our way from Carthagena to Santa Fe de 

 Bogota, we observed, that between Mompox and 

 Honda, in the valley of the great Rio Magdale- 

 na, the zancudoes darkened the air from eight 

 in the evening till midnight; that toward mid- 

 night they diminished in number, and were hid- 

 den for three or four hours ; and lastly that they 

 returned in crowds, and with a voracious ap- 

 petite, toward four in the morning. What is 

 the cause of these alternations of motion and 

 rest ? Are these animals fatigued by long flight ? 

 It is very rare at Oroonoko to see real gnats by 

 day ; while at the river of Magdalena we were stung 

 night and day, except from noon till two o'clock. 

 The zancudoes of the two rivers are no doubt 

 of different species ; are the compound eyes of 

 one of these species more affected by the splen- 

 dor of the solar light than the eyes of the 

 other ? 



We have seen, that the insects of the tropics 

 every where follow a certain standard in the 

 periods at which they alternately arrive and dis- 



