288 DR. H. GADOW ON EVOLUTION [Mar. 20, 



best they are subspecies, if not local races, or, worse still, only 

 pattern-varieties. 



In short, -we have here iioo forms in the actital jji^ocess of evolution, 

 which require only the accident of a physical separation belt — 

 which of course would not alter the remaining individuals — to 

 give them the standing of local races, but scarcely of subspecies 

 on account of the slight structural differences, and this because 

 they are still in the process of making ! 



It is faii-ly safe to consider the var. immutahilis as closely allied 

 to C. dep2)ei, perhaps as a larger form evolved from a more gene- 

 ralised clan of C. dejypei. On p. 319 the question is discussed 

 whether true links still exist between them, but none have been 

 found. It is therefore concluded that C. deppei and G. immuta- 

 hilis being practically coterminous in their wide range, their 

 differentiation from the hypothetical common stock had proceeded 

 far enough to turn them into "species," implying the disappearance 

 of links. In other words, these two forms, concerning each other, 

 are no longer in the act of being made *. This may mean either 

 that their divergence dates back a longer time, or that they have 

 divided the ground between them sufficiently well, leading lives 

 too different for competition, and too diverse in the ensuing- 

 reaction upon the surroundings, so that the differentiation has 

 proceeded more rapidly. The facts that C. deppei inhabits also 

 the Atlantic hotlands, where it meets the C. guttatus (from 

 which it is structurally and in pattern more widely removed than 

 from the C. immutabilis), and further, that C. dejjpei has such an 

 enoi-mous range southwards into South America, these circum- 

 stances rather favour the assumption that C deppei is an old form 

 and that the evolution of C. immutahilis is of an older date than 

 its splitting into the present striped and spotted or Pacific and 

 Atlantic races. Present species are older than sid>sp)ecies, and 

 these are older than their pi^esent races. 



On p. 305 the very pertinent question is discussed whether 

 the small G. deppei is always separable from the equally small 

 G. sexlineatus, the least differentiated, the most primitive of the 

 whole genus, of which, by a fortunate accident, it happens 

 to be the type. AVe there succeeded in singling out some 

 specimens of G. sexlineatus from Sauz near Chihuahua, and of 

 G. dep2)ei from South Guerrero, which apparently are not 

 separable ; but we had to explain these as cases of convergent 

 development, or, let us say, as due to the coincidence of the 

 variations of all the characters emjoloyed. Some valid reasons 

 were given to show that these Guei'rero clans aie local varieties 

 of the other suii'ounding G. deppei. The argumentation seems 

 satisfactory, but it would have been far less so, if these con- 

 vergent lizards had been taken in neighbouring districts, instead 



* The differences are, however, sometimes so small that, if, for instance, the 

 Cajones (text-fig. 81 E) or the Miahuichan specimens {cj. p. 326) were the onlj^ 

 representatives known of C. immutabilis, we should unhesitatingly treat them as a 

 subspecies of C. deppei ! 



