HA8EMAN, GEOGRAPHICAL DISTRIB UTION IN SOUTH AMERICA 71 



the germplasm and somaplasm or in each separately. For example, he 

 was able to increase the temperature in the laboratory at Chicago and 

 obtain forms of the potato beetle which lived in Mexico. Tower's work 

 shows almost beyond a doubt that when the same species of potato beetle 

 lived in different environmental complexes, similar variations were pro- 

 duced in similar environments. This is all that is required to explain 

 the similarity of certain genera and species of fishes which are found in 

 the Paraguay and Amazon, but not in the Parana, Uruguay or the coast- 

 wise streams of eastern Brazil. Furthermore, the requirement is not 

 great, because many of the genera and species of fishes are based on one 

 more or less spine, three to ten more or less scales in the lateral line, color 

 and position of spots and other trivial characters which are subject to a 

 wide range of so-called fluctuating variation. In fact, some of these 

 variations may even exist occasionally in the generalized widely distrib- 

 uted highland species from which the bulk of the ichthyological fauna 

 of the various river basins has evolved. 



Any one less familiar than the writer with the region in question would 

 not venture to state that identical evolution has taken place on such a 

 large scale in similar environments. As I have already shown, however, 

 no connection exists between the Paraguay and the Amazon. Accidental 

 overland and marine distribution is more absurd than identical evolution 

 from common highland stock, and even if the species got across, we 

 should still have to admit that they have remained almost the same in 

 the case of the Paraguay and the Amazon and have not in the case of 

 the Parana and Uruguay rivers, which belong to the same basin as the 

 Paraguay. To admit the latter is equivalent to admitting either that 

 identical evolution has taken place in the case of many genera and species 

 of fishes, or else to believing in the fixity of species in one locality and 

 not in another. Furthermore, the Sao Francisco has a connection with 

 the Amazon, and yet its cichlid fauna is composed of the three common 

 highland genera and species only. If a connection is needed to explain 

 the similarity of the Paraguayan fishes with the Amazon, I desire to ask, 

 Why has the Eio Sao Francisco only three species of cichlids? Why 

 is there a triple cichlid faunal region in the La Plata hasin ? Why have 

 the Paraguayan species remained identical with the Amazonian? Why 

 did not more of the Cichlidse of Eio Guapore enter the Paraguay ? My 

 answer to these questions is that similar environments have produced 

 some similar changes in the same germplasm, i. e., the highland genera 

 which are widely distributed, 34 and dissimilar environments have pro- 



M This does not at all imply the inheritance of acquired characters, for it can also 

 easily be a direct effect on the eggs, sperms or germplasm. 



