1903.] and Orthogenetic Variation in Lizards, etc. 119 



Summary of the Evolution of the Pattern (fig. 7). 



Longitudinal white stripes can be dissolved into spots, and this 

 breaking up proceeds from the tail forwards. On the other hand, pale 

 spots can by confluence produce longitudinal stripes, e.g., in Ameiva 

 and in the lines which appear in the centre field of C. striatus and 

 C. deppei. Another mode of the production of white stripes is the 

 concentration of the dark pigment along the borders of an existing 

 dark band, while new, colourless tissue grows in the middle of such 

 band, which ultimately is transformed into a white stripe flanked by a 

 dark one. Or, in the case of the unpaired spinal band, this process 

 may be reversed; dark pigment appearing in the centre of the 

 broadening white band, which thereby is split into two white stripes. 

 This process is repeated alternately, cf. in C. deppei, ranging from 8 to 

 11 stripes. 



Confluence of pale spots in a transverse direction, accompanied by a 

 massing of dark pigment along the newly-formed borders, leads, to a 

 pattern of cross-bars, cf. C. mexicanns. Uniform coloration is the 

 last, highest, stage attainable. 



Concerning Cnemiilophorus, the various lines of evolution are the 

 following ; assuming as the starting point a small form like the typical 

 C. sexlineatus with 6 strongly marked white stripes : 



1. In sandy terrain with sparse tufts of grass. Increased number of 

 sharply marked stripes with tendency to increase from 8 to 11 : 

 C. deppei. 



2. In the same terrain, but with less scanty vegetation. Usually 7 to 

 9 stripes which tend to break up into spots on the lower back, and 

 reduction of the lateral stripe : C. gnttatus striatus. 



3. In open tropical forest, with much undergrowth. Fading of the 

 lateral stripe ; dissolution of the other stripes into numerous small 

 spots, which disappear with age on the lower back : C. guttatus guttatus. 



4. On the open table-land, with scattered spiny shrubs and hedges. 

 Change of the young with 6 sharp stripes and pale spots on the dark 

 bands to a cross-barred pattern : (J. mexicanuj. 



5. Same localities as the last, but with more mixed vegetation. All 

 the lines are broken up into spots, in addition to those on the inter- 

 mediate parts : C. bocourti, a spotted race of C. mexicanus. 



There can be no doubt about it that in the genus Cnemidophorus 

 the permanently striped condition is the original, while the spotted 

 is a secondary modification, upon which in turn follows the formation 

 of cross-bars. Both the spotted and the barred forms have a tendency 

 towards uniform coloration. This ultimate and highest stage is 

 partly reached by C. bocourti and C. guttatux, without the interposition 

 of a barred stage. Parallel cases are Cope's C. semifasdcUus and 

 foseel&tus rubidus, which are terminal side issues of the typically striped, 



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