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



best they are sub.species, if not local races, or, worse still, only 

 pattern- varieties . 



In short, im have here two forms in the actual process of evolutiori, 

 which reqnii-e 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 structui'al differences, and this because 

 they are still in the process of making ! 



It is fairly safe to consider the var. immutabilis as closely allied 

 to C. depjjei, pei'haps as a lai'ger foi-m evolved from a more gene- 

 ralised clan of C. dejjpei. On ]). 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 C. ionmiUa- 

 hills 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, 

 nre 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 diveise in the ensuing 

 reaction upon the suiroundings, so that the differentiation has 

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

 the Atlantic hotlands, where it meets the C. guttatas (fi'om 

 which it is structurally and in pattern more widely removed than 

 from the C. immutabilis), and farther, that C. deppei has such an 

 enormous range southwards into South America, these circum- 

 stances rather favour the assumption that C . depjiei in an old form 

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

 its splitting into the present stiiped and spotted or Pacific and 

 Atlantic races. Present sj)ecies are older than subsjyecies, and 

 these are older than their prresent races. 



On p. 305 the very pertinent question is discussed whether 

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

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

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

 to be the type. "We there siicceeded in singling out some 

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

 C. deppei from South Guerrei-o, which appai-ently 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 

 valuations of all the characters employed. Some valid I'casons 

 were given to show that these Gueii-ero clans are local varieties 

 of the other surrounding C. dejjpei. The argumentation seems 

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

 vergent lizards had been taken in neighbouring districts, instead 



* Tlie dift'ereiices are, however, sometimes so small that, if, for instance, the 

 Cajones (text-fig. 81 E) or the Miahuichaii specimens (e/. p. 326) were the oiilj^ 

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

 subspecies of C. deppei ! 



