132 The Naturalist in La Plata. 



for then an immediate burst of cold wind is con- 

 fidently looked for. In the expressive vernacular 

 of the gauchos the large dragon-fly is called hijo del 

 pampero son of the south-west wind. 



It is clear that these great and frequent dragon- 

 fly movements are not explicable on any current 

 hypothesis regarding the annual migrations of birds, 

 the occasional migrations of butterflies, or the mi- 

 grations of some mammals, like the reindeer and 

 buffalo of Arctic America, which, according to Rae 

 and other observers, perform long journeys north 

 and south at regular seasons, " from a sense of 

 polarity." Neither this hypothetical sense in 

 animals, nor " historical memory " will account for 

 the dragon-fly storms, as the phenomenon of the 

 pampas might be called, since the insects do not 

 pass and repass between " breeding and subsistence 

 areas," but all journey in a north-easterly direction; 

 and of the countless millions flying like thistle- 

 down before the great pampero wind, not one solitary 

 traveller ever returns. 



The cause of the flight is probably dynamical, 

 affecting the insects with a sudden panic, and com- 

 pelling them to rush away before the approaching 

 tempest. The mystery is that they should fly 

 from the wind before it reaches them, and yet travel 

 in the same direction with it. When they pass 

 over the level, treeless country, not one insect lags 

 behind, or permits the wind to overtake it ; but, 

 on arriving at a wood or large plantation they 

 swarm into it, as if seeking shelter from some 

 swift-pursuing enemy, and on such occasions they 

 sometimes remain clinging to the trees while the 



