348 Laceriiihv. 



diviJeJ into three sections, tlie first and second of wliich are South 

 African and no doubt derived from South African forms of the 

 section Mesalhia, whilst the third is Asiatic, like the members of the 

 Section Eremias proper, to which these species stand in the same 

 relation as the African forms to one another. 



In spite of its diphyletic origin and notwithstanding its close rela- 

 tion to, and intergradation with, Eremias, I can see no objection to 

 the retention of this genus in the sense here taken ; but it is well to 

 divide it into sections which express the relationship of the species. 



In fact the genus Scaptira is simply made up of modified forms of 

 Eremias agreeing in the stronger lateral serration of the digits and 

 thus brought together as a result of convergence, such as accounts for 

 many of our taxouomic divisions. If, however, objection should be 

 felt to the course here followed, I would suggest uniting the two 

 genera into one, keeping up the diffeieut sections as here defined, 

 ratlier than a further multiplication of the genera. 



That we are here in presence of a case of parallelism, through 

 adaptation to desert life, is, I think, undeniable. The question 

 whether the genus Scajitira, in the sense here taken, is justified is one 

 of convenience versus principle,* e. g. whether it is advisable to group 

 together in one genus several species deiived from one type which 

 became differentiated along diverging lines, the ends of which come to 

 resemble each other, as has often been discussed in the case of the 



• " The question . . . as to the single or multiple origin of genera is at 

 bottom rather a question about woi'tls than about things, and the answer 

 which we make to it will to a great extent depend upon the view taken as to 

 the definition of the word genus. If we make classification an expression of 

 real relationship, and not of mere similarity of structure, as should certainly 

 be the end projjosed, then it is obvious that all the species of a genus must be 

 more nearly allied to each other than they are to those of any other genus, 

 recent or extinct. But as genei-a are at present employed and in the existing 

 state of knowledge, such an exact expression of relationship is impracticable, 

 as that would necessitate a minute knowledge of the phylogeny of each 

 species, such as we are very far from possessing." (AV. B. Soott, Journ. of 

 Morphol. v, 1891, p. 301.) 



'• It may be the general rule, as almost certainly has often happened, that a 

 new genus arises by the separate assumption of the new character by several 

 species of the ancestral genus, rather than through the rapid diversification of 

 a single species, though, no doubt, parallel and divergent modification are both 

 very frequent and important jjrocesses. Dr. Eigeumann concludes from his 

 study of South American fresh-water fishes that a certain new genus is even 

 now in process of origin through the transformation of several species of an 

 older genus, which in different parts of the continent are simultaneously, but 

 independently, taking on the new character." (W. H. Scott, History of Land 

 JIammals in the Western Hemisphere [Xew York, 1913], p. 054.) 



