ANIMAL MIGRATIONS 367 
naturalists to certain transits or migrations of the 
adult insects across the Amazon, such as have 
already been noticed by Messrs. Edwards, Wallace, 
and Bates, and perhaps by other travellers. The 
first time I fell in with such a migration was in 
November 1849, near the mouth of the Xingii, 
when I was travelling up the Amazon from Para to 
Santarem ; and it is thus sketched in my Journal : — 
. . . As we returned to the brig we saw a vast 
multitude of Butterflies flying across the Amazon, 
from the northern to the southern side, in a direction 
about from N.N.W. to S.S.E. They were evidently 
in the last stage of fatigue : some of them attained 
the shore, but a large proportion fell exhausted into 
the water, and we caught several in our hands as 
they passed over the canoe. They were all of 
common white and orange-yellow species, such as 
are bred in cultivated and waste grounds, and having 
found no matrix whereon to deposit their eggs 
to the northward of the river (the leaves proper 
for their purpose having probably been already 
destroyed, or at least occupied, by caterpillars), were 
going in quest of it elsewhere." 
The very little wind there was blew from between 
E. and N.E.; therefore the butterflies steered their 
course at right angles to it ; and this was the case in 
subsequent flights I saw across the Amazon, although 
when the wind was strong the weaker- winged insects 
made considerable leeway, and would doubtless most 
of them succumb before reaching land. But the 
most notable circumstance is that the movement is 
always S02ithward, like the human waves which from 
the earliest times seem to have surged one after the 
other over the whole length of America, generating 
