EVIDENCE CONCERNING EVOLUTION. 



"5 



either that the condition is due to chance, and does not really represent the 

 orderly development of species which it would seem to, or that the data of 

 variation and distribution give the true order of evolution. It must be ad- 

 mitted that the data do permit of the construction of a plausible scheme of 

 the phylogenetic relationship of these species, such as the one shown in text- 

 figure 4. 



A scheme like that given in text-figure 4 is highly plausible, and is apt to so 

 strike one's fancy that other possibilities are ignored, as, for example, the one 

 that the relations suggested by the data employed are due to chance, and have 

 no real meaning. 



DISTINQUENDA 



\ 

 PUDICA 



\ 



OBLITERATA 



TVPOQRAPHICA 

 LINEOLATA 



CALCEATA CACICA 



^ / 



DILECTA NITIDICOLLIS 



NOVEMLINEATA 



FLAVITARSIS 



HYPOTHETICAL ANCESTOR 



Text-figure 5. Scheme of the phylogenetic development of the dilecla group, 

 based upon the data of its distribution and variation. 



The dilecta group consists of a series of species which are widely dissem- 

 inated and variable and nearly as numerous as those in the lineata group. On 

 plate 12 is represented their distribution over northern Central America and 

 Mexico. Here also are found series of species which in their geographical 

 distribution and their variations show conditions similar to those in the lineata 

 group. The species flavit arsis from Guatemala, nitidicollis from Chiapas, 

 and cacica from the Atlantic slope represent, in as far as their known distribu- 

 tion and variations can indicate, a line of species differentiation from highland 

 to lowland and in a given direction. Another series consists of the species 

 dilecta from the Oaxaca-Guerrero highlands and northward over the South 

 Mesa of Mexico, with its lowland modification, calceata, and its close allies to 

 the north, lineolata and typographica. Still another series is that made up of 

 the species novemlineata, oblitcrata, distinguenda, and pudica. It has not 

 been possible to obtain as full data of the distribution and variation in the 

 dilecta group as in the lineata group, but all known facts point to species 

 formation in certain directions over the continent one line of differentiation, 

 that found in the series Havit arsis, nitidicollis, and cacica extending to the 

 north and eastward ; another, represented by dilecta and its allies, spreading 

 northward, and so on. The scheme of the phylogeny of this group, shown 

 in text-figure 5, is based upon its distribution and variation. 



