22 THE AMERICAN CHARACIDAE. 



when we consider the very probable long separation of the African and Ameri- 

 can sections of the family, and that the present forms in Africa and America 

 have probably independently evolved in the two continents from a common 

 rudiment. As von Ihering first pointed out for animals in general, and as I 

 have more particularly shown for the fishes, there has probably been no inter- 

 migration between the two continents since or previous to the early Tertiary. 



Before the Tertiary von Ihering has postulated an Archhelenic continent 

 between Africa and South America from which the two continents probably 

 derived the ancestors of the Characins among other elements of the present 

 fauna. 



It is known that the Characins have inhabited South America since the 

 early Tertiary at a time when the tropical part of the continents probably con- 

 sisted of two islands, one occupying the Guianas, the other the plateau of eastern 

 Brazil. From this small area and from the primitive group of Characins 

 inhabiting it, the continent and family grew contemporaneously to their present 

 proportions. They spread from these centers over the developing continent till 

 they met unfavorable climatic conditions in the south, and high mountains 

 or contestants in the north. They spread southward in decreasing numbers 

 to and beyond the barren areas of Argentine to the edge of Patagonia, and they 

 spread northward decreasing rapidly in numbers at Panama, only one of them 

 reaching the United States, three southern Mexico, and three the Motagua River. 



In South America they have always flourished, their only competitors in the 

 rivers of the growing continent being the indigenous fishes contemporaneously 

 developing from similar small rudiments. They have never been hampered or 

 affected by intrusive elements. Their territory has from the first been unap- 

 proachable to foreign fresh-water fishes, and the marine species that have accli- 

 mated themselves have not diverged to any extent from their marine relatives. 



The African section, on the other hand, came into competition with emi- 

 grants from India, and, according to Boulenger, the affinity of the entire Afri- 

 can fauna with Asia, "is much greater than with America which is emphasized 

 by the fact that the genera in the two first named regions are identical, while 

 America possesses genera very closely related but not identical with those of 

 Africa." 



The American Characins have diverged, as stated before, in the most amaz- 

 ing manner in almost all possible ways towards diverse forms assumed by fishes. 

 Some are long and slender, some nearly as deep as long, some spindle-shaped, 

 others compressed. It is, however, in the teeth and alimentary canal that we 

 find the greatest diversity, as has already been pointed out, and as will be 



