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INDIANA UNIVERSITY 



been noticed, the characters were either not assorted by chance, 

 or there was a distinct weeding out of certain possible combina- 

 tions whenever they appeared. It is possible that some of these 

 predicable combinations exist but have not yet been discovered. 



The Tetragonopterinee are now at their prime; they abound in 

 individuals and species, and they live in the greatest possible varie- 

 ties of environment to be found in tropical America. (What is 

 true of the Tetragonopterinae, is true, of course, of the Characidag 

 to which they belong, but it is not true of any other subfamily of 

 the Characidfe.) These conditions jiiake a study of the lines and 

 methods of evolutions profitable, even if the causes for them are 

 not at present obvious. 



The one fact that forces itself most conspicuously upon the 

 attention is that the same character present in different members of 

 the Characins in general and in the Tetragonopterinae in parti- 

 cular may have arisen independently several times. 



The lateral line may become and has become incomplete re- 

 peatedly, and is undergoing that change now. 



Three series of teeth have been derived from two, several times, 

 and the process is going on now. 



The caudal has possibly become scaled a number of times, and 

 it may be that the condition is being produced now in certain 

 species of Astyanax and Hyphessobrycon. 



Teeth have developed along the entire maxillary a number of 

 times, and the process is still in operation. The teeth have disap- 

 peared entirely from the maxillary a number of times, and it is 

 safe to say that this end result is being approached in different 

 series now. 



Scales have become crenate, or ctenoid, more than once. A 

 single series of teeth has given rise to two series, or of two series 

 one has become lost several times, and the process is going on now. 



The second tooth of the dentary has moved forward several 

 times. 



The predorsal line, fully scaled in many species, has become 

 partly naked several times. 



The second suborbital has expanded to touch the preopercle 

 many times, and is making that change now in several instances. 



The adiopose fin has disappeared in diverse types, and the pro- 

 cess of its disappearance can also be seen at the present time. 



The anal has increased or decreased in length in many differ- 

 ent genera or species as a glance at the variation of the same species 

 in different localities will show. 



