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



The general applicability of Eimer's " laws " has been tested with 

 favourable results in all classes of vertebrata, although naturally in 

 many cases the detailed investigation is obscured by caenogenetic 

 omissions and other modifications. 



Cope* has repeated Eimer's observations by the study of several kinds 

 of the American lizard-genus Cuemidophorus, and he has illustrated several 

 successive changes from stripes to cross-bars in C. tesselatus and C. gularis. 

 But he has split the whole genus into a bewildering number of species 

 and sub-species, not allowing sufficient scope for individual variation, 

 and he has apparently not exemplified his points on specimens from 

 the same locality. An attempt to study these and similar changes 

 minutely and in series, and to connect them with the prevailing 

 conditions of the surroundings, has hitherto not been made. 



I have been fortunate during the last summer in collecting material 

 sufficient to show, first, the amplitude of individual variation ; secondly, 

 that there exist in the various kinds of Cnemidophonu several modes of 

 attaining the same end, that each of these modes may occur, and proceed 

 to a moderate extent individually, carrying the individual out of its 

 normal way, and lastly, that some of these changes seem to be governed 

 by the physical conditions (constitutional or organic, and the prevailing 

 features of the terrain), while sexual selection plays none, and natural 

 selection but a secondary part. 



Such inquiries cannot be made unless the exact conditions of the 

 terrain, and the habits of the creatures are observed. My collections 

 and observations were made in steaming hot tropical forests, in hot 

 and dry lowlands, and on the more temperate table-lands of Southern 

 Mexico. My material has been compared with that in the National 

 Collection, and I have to thank Mr. Boulenger for his ever-ready 

 invaluable help and advice. 



II. The Structural Variations and the Mutual Affinities of Various 

 Kinds of Cnemidophonu. 



It is a tedious, but necessary, preliminary to record the amplitude of 

 the so-called structural variations within the recognisable kinds of 

 Cnemidophonu Whether these be called species, sub-species, or races 

 is a matter of personal inclination, but the smaller the structural 

 differences, the more significant will be the differences in pattern and 

 coloration in such closely allied forms, provided these live under 

 other physical conditions. All the various Cnemidopliorus and Ameiva 

 live on the ground, never climbing trees hunting for insects. 



I recognise five definable forms of CnemidopJi onis as occurring in Southern 



* 'Amer. Phil. Soc. Proc.,' 1885, p. 283; and ' Report of the U.S. National 

 Museum,' 1898, p. 5G9. 



