28 A JOURNEY IN BRAZIL. 
Their upper part is usually broken by waterfalls, their 
lower course being more level ; probably in the lower 
courses of these rivers we shall find fishes similar to those 
of the short coast streams, while in the higher broken 
waters we shall find distinct faunae." The lecture closed 
with some account of the excursions likely to be undertaken 
in the neighborhood of Rio de Janeiro on arriving, and with 
some practical instructions about collecting, based upon Mr. 
Agassiz's personal experience.* 
* On account of the many exploring expeditions for which the Bay of 
llio de Janeiro has been a favorite port, it has acquired a special interest for 
the naturalist. It may seem at first sight as if the fact that French, English, 
German, Russian, and American expeditions have followed each other in this 
locality, during the last century, each bringing away its rich harvest of speci- 
mens, by diminishing its novelty would rather lessen than increase its interest 
as a collecting ground. On the contrary, for the very reason that the speci- 
mens from which the greater part of the descriptions and figures contained in 
the published accounts of these voyages were obtained from Rio de Janeiro 
and its neighborhood, it becomes indispensable that every zoological museum 
aiming at scientific accuracy and completeness should have original specimens 
from that very locality for the identification of species already described. 
Otherwise doubts respecting the strict identity or specific difference of speci- 
mens obtained on other parts of the Atlantic shore, not only in South America 
but in Central and North America, may at any time invalidate important gen- 
eralizations concerning the distribution of animals in these seas. From this 
point of view, the Bay of Rio de Janeiro forms a most important centre of 
comparison, and it was for this reason that we made so prolonged a stay there. 
Although the prospect of discovering any novelties Avas diminished by the 
extensive investigations of our predecessors, I well knew that whatever we 
collected there would greatly increase the value of our collections elsewhere. 
One of my special aims was to ascertain how far the marine animals inhabiting 
the c^ast of Brazil to the south of Cape Frio differed from those to the north 
of it, and furthermore, how the animals found along the coast between Cape 
Frio and Cape St. Roque differed from or agreed with those inhabiting the 
more northern shore of the continent and the West Indian Islands. In the 
course of the following chapters I shall have occasion to return, more in de- 
tail, to this subject. L. A. 
