xxin 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 tin: 

 most notable circumstance is that the movement is 

 always southward, like the human waves which from 

 the earliest times seem to have surged one after the 

 other over the whole length of America, generating 



