368 NOTES OF A BOTANIST CHAP. 



after a time a reflux northwards, as in the case of the 

 empire of the Incas. . . . 



Since my return to England I have read Mr. 

 Bates's graphic description of a flight of butterflies 

 across the Amazon below Obidos, lasting for two 

 days without intermission during daylight. These 

 also all crossed in one direction, from north to south. 

 Nearly all were species of Callidryas, the males of 

 which genus are wont to resort to beaches, while 

 the females hover on the borders of the forest and 

 deposit their eggs on low-growing, shade-loving 

 Mimosae. He adds, " The migrating hordes, so far 

 as I could ascertain, are composed only of males." 

 It is possible, therefore, that in the flights witnessed 

 by myself the individuals were all males in which 

 case the flights should probably be looked upon not 

 as migrations but dispersions, analogous to those of 

 male ants and bees when their occupation is done, 

 and they are doomed by the workers to banishment, 

 which means death. In the case I am about to 

 describe, however, the swarms certainly comprised 

 both sexes > although I know not in what proportion ; 

 and their movements were more evidently dependent 

 on the failure of their food. 



In the year 1862 I spent some months at 

 Chanduy, a small village on the desert coast of the 

 Pacific northward of Guayaquil, where one or two 

 smart showers are usually all the rain that falls in a 

 year ; but that was an exceptional year, such as 

 there had not been for seventeen years before with 

 heavy rains all through the month of March, which 

 brought out a vigorous herbaceous vegetation where 

 almost unbroken sterility had previously prevailed. 



1 Naturalist on the Amazons, vol. i. p. 249. 



