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Show 1906.] IN MEXICAN LIZARDS. 299 new varieties, races, &c. are formed, or at least initiated. Whether they can hold their own, can become common, or predominant, depends upon the test of life and time. In any case, when we speak of them as new varieties or races <fec, we thereby but register the fact that the characters of these lizards in certain localities average differently from what we are pleased to consider the normal, more universal stock. On the other hand, where environmental conditions are stable, or when the new homes imply no bionomic change, there should be no reason for shaking up the organism ; it should arrive at a settled condition, and the only changes, if any, should be very gradual and orthogenetic, following the law of improvement. It follows from these considerations, that the evolution of new species should be most active, most obvious in varied, not in monotonous districts. It also follows that change of environmental conditions need not imply migration, or spreading, but change of conditions in loco. It is a kaleidoscopic process-a stirring up, and there are new combinations, some of transient existence, others are obvious failures, others are lucky hits which should be the most successful according to all canons. They seem to fall into the category of " mutations," but to a rather mild extent, since the game is played fairly with all the pieces or characters upon the board, none more and none less. The game has been played incessantly and in many places by these lizards, hence the possibility of the occurrence of the same combinations at different times and places ; and such coincidences become probabilities when the performers are of a kindred stock and play under similar conditions those subtle rules and influences and traditions which Nature is able to " corriger la fortune." The distressingly laborious examination of half a thousand specimens of Cnemidophorus has not been in vain, since it has revealed not a few instances which are favourable to the interpretations and to the general conclusions given in this paper. None amounts to proof, but even an occasional glimpse may lead to a path into and eventually out of a tangle which hides quagmires and precipices with its luxuriant and often thorny growths, but which above all attracts us by its glorious and mysterious beauty. Definition of the genus C N E M I D O P H O R U S Wagier, pt.; Boulenger, Cat. Lizards, ii. 1885, p. 360.-Swift-running, strictly humivagous Tejida?, with a long, narrow arrow-headed tongue, not retractile into the base; lateral teeth compressed, bi- or tricuspid; head covered Avith large regular shields; anterior nasals in contact with each other; dorsal scales granular; ventrals large, forming regular rows; with a double collar-fold ; with femoral pores; tail round ; eyelids and ear-opening well developed. |