290 ANNALS NEW YORK ACADEMY OF SCIENCES 



In general, so far as I can judge, the Lacertilia lend no support to 

 the theories of transoceanic bridges. Their widespread insular distri- 

 bution must in some cases, and may in most others, be explained by 

 over-sea transportation. They lend some support to late Tertiary eleva- 

 tions to the continental shelf line so as to include the continental islands 

 and to a line of separation in the East Indies which some, but not all, 

 were able to cross; those which did succeed in crossing it spread widely 

 through Australia, indicating more continental conditions, and also indi- 

 cating in these families a capacity for crossing marine barriers which 

 enabled some of them to reach Madagascar, New Zealand and various 

 Pacific islands. 



The ratio of their abundance in regional faunae is apt to be inversely 

 to the full development of mammalian life. Where mammals are scanty, 

 as in oceanic islands, lizards partly take their place ; and this is true of 

 some continental regions as well as of oceanic islands. In the typical 

 continental fauna, the lizards are largely restricted to desert or rocky 

 habitat and are of small size. Yet these last are the most typical mem- 

 bers of the order.. They show what its primary adaptation was. Various 

 readaptations appear, to fossorial, to aquatic, to arboreal or to terrestrial 

 forest life, repeated again and again in different families and causing 

 frequent parallel divergencies from the primary type. This primary 

 type, I regard as an adaptation to a Mesozoic arid period. The moist 

 uniform climatic phase of the early Tertiary would tend to develop large 

 forest living and aquatic forms and restrict and provincialize the more 

 typical lizards. During the middle and later Tertiary, the typical lizards 

 would expand and multiply in numbers and variety, but, on account of 

 their lack of adaptability to cold climate, their evolution was not so 

 much a successive series of dispersals from a Holarctic center, as a 

 provincial evolution from the arid centers of the great continents. Such 

 a priori hypotheses are of little value, however, except as confirmed, 

 modified or refuted by detailed study of the affinities and geographic 

 distribution of the genera of each family, checked by a wider knowledge 

 and more thorough study of the fossil forms. Until the fossil Lacertilia 

 have been thoroughly studied and their affinities authoritatively esti- 

 mated, any conclusion whatsoever as to the evolution and distribution of 

 the order remains highly hypothetical. 



Dr. Gadow's recent study^^* of the distribution of Cnemidophonis and 

 its interpretation is an excellent example both of the value of such de- 

 tailed studies and the need of carefully distinguishing between what the 



"* H. Gadow : "A Contribution to the Study of Evolution based upon the Mexican 

 Species of Cnemidophorus," Proc. Zool. See. London, vol. 1, pp. 277-375. 1906. 



