VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 11 
seivations respecting the distribution of species in the Euro- 
pean rivers. I have found that, while some species occur 
simultaneously in the many upper water-courses which com- 
bine to form the Rhine, the Rhone, and the Danube, most 
of them are not found in the lower course of these rivers ; 
that, again, certain species are found in two of these water- 
basins and do not occur in the third, or inhabit only one 
and are not to be met in the two others. The brook trout, 
for instance {Salmo Fario), is common to the upper course 
and the higher tributaries of all the three river-systems, 
but does not inhabit the main bed of their lower course. 
So it is, also, and in a more striking degree, with the Salm- 
ling (Salmo Salvelinus). The Huchen (jSalmo Huclio) is 
only found in the Danube. But the distribution of the 
perch family in these rivers is, perhaps, the most remark- 
able. The Zingel (Aspro Zingel) and the Schraetzer (Aceri- 
na Schrcetzer) are only found in the Danube ; while Acerina 
cernua is found in the Danube as well as in the Rhine, 
but not in the Rhone ; and Aspro asper in the Danube as 
well as in the Rhone, but not in the Rhine. The Sander 
(iMcwp&rea Sandra) is found in the Danube and the other 
larg'e rivers of Eastern Europe, but occurs neither in the 
Rhine nor in the Rhone. The common perch (Perca flu- 
viatilis)) on the contrary, is found both in the Rhine and 
Rhone, but not in the Danube, which, however, nourishes 
another species of true Perca, already described by Schaeffer 
as Perca vulgaris. Again, the pickerel (JEsox Lucius) is 
common to all these rivers, especially in their lower course, 
and so is also the cusk (Lota vulgaris). The special dis- 
true for nearly three thousand miles of its course is true also for the head-waters 
of the Amazons ; indeed, other investigators have already described some spe- 
cies from its higher tributaries differing entirely from those collected upon this 
expedition. 
