122 Dr. H. Gadow. Evolution of the Colour-pattern [May 22, 



exactly the process which we observe in these lizards. Why are the 

 continuous lines broken, and why do secondary spots appear in the 

 intermediate fields ? Because the epigastric and cardinal veins are 

 superseded by intercostal, i.e., transverse vessels, and the linear disposal 

 of pigment is incessantly interfered with by the shadows and lights of 

 the living, therefore moving animal. And it is infinitely more natural 

 that these shadows and lights will fall cross-ways upon a cylindrical 

 body than lengthwise. It may be a mere coincidence, but it seems 

 significant that longitudinal stripes are the prevalent pattern mostly in 

 small species, and that to take one of our cases, C. mexicanus loses these 

 stripes when it passes beyond the size of C. zexlineatus or C. deppei. 



Next comes the question why do any of these lizards retain their 

 stripes if it is the natural course of onward evolution to lose them 1 

 The answer can only be that small-bodied lizards, living amongst sparse 

 tufts of grass have their pattern less interfered with than larger species, 

 that the linear marking is even enhanced by the distribution of light, 

 and last, not least, that natural selection raises no objection to such a 

 case of epistasis. If these should afford protective advantages, then it 

 will be all the more likely that communities of individuals, wherever 

 they happen to live under the same conditions, will consolidate them- 

 selves into the same kind of race, and if there are also " structural " 

 changes, then the systematist will condescend to call them sub-species, 

 or even species. 



This brings us to a consideration of the structural variations men- 

 tioned on pp. Ill and 112. These variations neither go together nor 

 with the evolution of the colour-pattern. One individual may have 

 reached perfection in the matter of femoral scales, and in colouration, 

 while it lags behind in other features, and vice versA, in kaleidoscopic, 

 endless combinations and permutations. For some of these modifica- 

 tions we can at least imagine their use. For instance, the protective 

 advantage of the plates, enlarged in size and in numbers, which encase 

 those surfaces of the limbs which come into contact with obstructions 

 like thorny undergrowth, sharp blades of grass, &c. The collar, and 

 the rest of enlarged scales on the middle of the throat, may be in 

 relation to the mode of pouncing upon their prey, and rushing through 

 obstructions. 



But, after all, the detail of these variations presents such minute 

 differences that immediate advantage, or weeding out, is out of the 

 question. The fact remains that individuals of C. guttatus, possessed of 

 only 20 femoral pores, grow up to propagate the species in exactly the 

 same locality as those which can boast of 25 pores, and have 7 instead 

 of 11 or 12 rows of femoral plates. Where can be the disadvantage 

 of the retention of a few minute granules between the larger collar- 

 scales, as described in C. deppei ? The same applies to the minute 

 changes of the colour-pattern. There are specimens of C. deppei with 



