TEIID LIZAItDS OV THE GENUS CNEMIDOPHORUS 



75 



differences from (julai-is, it is considered to be a deriviti^'e from the 

 ancestral stock of the modern deppi/'. Its iiumncr of oriiiin is a 

 matter of some doubt us indicated in tlie discussion of its affinities. 

 Because of its coextensive distribution Avith the parent form, specia- 

 tion by mutation, in phice, is at first sight indicated. It is thought, 

 however, that the natural geological changes that have occurred in 



Figure IS. — Map showing distribution of forms of deitii group 



the region of Central America and Mexico, in this case at the isthmus 

 of Tehuantepec, may have permitted speciation during a temporary 

 period of isolation. Even this theory is thought to be in accordance 

 with the principle of speciation by mutation, which in itself repre- 

 sents the sort of variation that is thought to give rise to new forms. 

 For a discussion and diagram of the possibilities of this theor}^ as 

 applied to deppii and guttatus see pages 73 and 74. 



