344 A JOURNEY IN BRAZIL. 
la, where Mr. Agassiz wishes to make another collection of 
fishes. It may seem strange that, after having obtained, 
nearly five months ago, very large collections from the Ama- 
zons itself at this point, as well as from, the lakes in the 
neighborhood, he should return to the same locality, instead 
of choosing another region for investigation. Were his 
object merely or mainly to become acquainted with the end- 
less diversity of fishes he now knows to exist in this im- 
mense fresh-water basin, such a repetition of specimens from 
the same locality would certainly be superfluous, since it is 
probable that a different point would be more prolific in new 
species. The mere accumulation of species is, however, 
entirely subordinate to the object which he has kept in view 
ever since he began his present researches, namely, that of 
ascertaining by direct observation the geographical range of 
the fishes, and determining whether their migrations are so 
frequent and extensive as they are said to be. I make an 
extract from Mr. Agassiz' s notes on this subject. 
" I have been frequently told here that the fishes were 
very nomadic, the same place being occupied at different 
seasons of the year by different species. My own investiga- 
tions have led me to believe that these reports are founded 
on imperfect observations, and that the localization of species 
is more distinct and permanent in these waters than has been 
supposed ; their migrations being, indeed, very limited, con- 
sisting chiefly in rovings from shallower to deeper waters, 
and from these to shoals again, at those seasons when the 
range of the shore in the same water-basin is affected by 
the rise and fall of the river ; that is to say, the fishes 
found at the bottom of a lake covering perhaps a square 
mile in extent, when the waters are lowest, will appear near 
the shores of the same lake when, at the season of high 
