368 NOTES OF A BOTANIST 
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 ^/la^ 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. 
^ Naturalist on the Amazons, vol. i. p. 249. 
