24 



INDIANA UNIVERSITY 



Hemibrvcon, Deuterodon, and the larger genera are probably also 

 polypliyletic. 



Since it is difficult, or impossible, to say in any case which of 

 the given characters has appeared first, it is extremely difficnlt 

 to iDoint out lines of evolntion leading to different genera or species. 

 We can only insist that certain innate possibilities may become 

 actualities anywhere along the line, possibly wherever they may 

 prove advantageous, though the advantage, to say the least, is 

 not always obvious. 



We may be permitted to assume that the more frequent charac- 

 ter is the primitive one, although this is certainly not always a 

 safe assumption. 



In recent years it has been fashionable to assign causes for 

 certain observed phenomena. This has led to the long-drawn out 

 discussion of Lamarckism, Neo-lamarckism, Darwinism, Ortho- 

 genesis, etc. Without for the moment entering into the reasons, 

 it may be worth while to give several instances of each of a few 

 of the many changes that have evidently happened repeatedly, or 

 fire happening frequently now. 



The common possessions of all members of the Tetragono- 

 pteringe enumerated above, permit us to picture the ancestral type 

 of the subfamily. In brief, it must have been a fish similar in 

 most characters to Astyanax fasciatiis Cuvier. This species, be- 

 sides possessing all the characters common to all members of the 

 subfamily, possesses also many of those positive (as contrasted 

 with absent) characters enumerated for the family, and lacks* 

 some characters, like the highly specialized scaling of the ventral 

 surface, ctenoid scales, extreme length of anal, extreme develop- 

 ment of second suborbital, which are evidently highly specialized 

 characters in a few of the genera. It is more widely distributed 

 than any other species and has given rise to numerous variations. 



It represents an average in length of head (4.3), depth, (2.6-3) ; 

 length of anal (about 30) ; scales (about 38) ; size of eye (2.5-3) ; 

 general shape (compressed subfusiform) ; position of dorsal (its 

 base being in the space above the origins of the ventral and anal) ; 

 size of mouth ; and the characters of the teeth. The fossil fishes 

 found at Taubate — south of Rio de Janeiro — are similar to it in 

 most characters. They are a little larger and may be members 

 of the genus Brycon. In all but the teeth, they are very similar 

 to Asiiiana.r fasciatus. Their teeth have not been examined. 



Without attempting to follow the lines of evolution from the 

 Asfyauax fasciatus type of the genera now dominant, we can 



