Cli. IX.] MIGEATIOXS OF BUTTERFLIES. 153 



millions of individuals, comprising many different 

 species and genera. The beautiful tailed green and 

 gilded day-flying moth ( Urania kilns) also joins in this 

 annual movement. "When in Brazil, I observed similar 

 flights of butterflies at Pernambuco and Maraiiham, all 



O * 



travelling south-east. Mr. R. Spruce describes a migra- 

 tion which he witnessed on the Amazons, in November, 

 1849, of the common white and yellow butterflies. They 

 were all passing to the south-south-east.* Darwin 

 mentions that several times when off the shores of 

 Northern Patagonia, and at other times when some 

 miles off the mouth of the Plata, the ship was sur- 

 rounded by butterflies; so numerous were they on 

 one occasion, that it was not possible to see a space 

 free from them, and the seamen cried out that it was 

 "snowing butterflies." t These butterflies must also 

 come from the westward. I know of no satisfactory 

 explanation of these immense migrations. They occurred 

 every year whilst I was in Chontales, and always in the 

 same direction. I thought that some of the earlier 

 flights in April might be caused by the vegetation of the 

 Pacific side of the continent being still parched up, 

 whilst on the Atlantic slope the forests were green and 

 moist. But in June there had been abundant rains on 

 the Pacific side, and vegetation was everywhere growing 

 luxuriantly. Neither would their direction from the 

 north-west bring them from the Pacific, but from the 

 interior of Honduras and Guatemala. The difficulty is 

 that there are no return swarms. If they travelled in 

 one direction at one season of the year, and in an oppo- 



* " Journal of the Lmnasan Society," vol. ix. 

 f " Naturalist's Voyage," p. 158. 



