VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 11 



servations 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 Hucho) 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 tSchrcetzer) 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 

 (Lucioperca Sandra) is found in the Danube and the other 

 large 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 (Esox Lucius) is 

 common to all these rivers, especially in their lower course, 

 and so is also the cusk (Lota vulgaris). The special dis- 



truc 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. 



