THE DISTRIHUTION AND CHARACTERS OF REPTILES. 245 



the case, the various forms being connected together by various 

 grades of intermediates. 



De Varies found that his new " elementary species " (which 

 correspond in degree to what we should call constant varieties) 

 appeared within the very home of the parent form from which 

 they arose, and he says, " Many distinct species (his elementary 

 species) can and do exist side by side in the same range, and are 

 in fact found to be heaped up in the centre of their area of distri- 

 bution, but more scattered at the periphery." Now it is obvious 

 that such a mode of evolution is not likely to have efifected the 

 origin of the great majority of our species, for they are geo- 

 graphically separated, but it is possible that mutational evolution 

 may explain the various cases of closely allied species living 

 together in the same environment. However, if we seek for 

 characters which are essentially mutational, it is most difficult to 

 find a clear case. The two green water snakes Chlorophis natal- 

 ensis and C. hoplogaster are often found in the same localities : 

 the former has along each ventral scale of the body a distinct 

 keel on each slide, whilst the latter is described as having per- 

 fectly smooth ventral scales. Formerly I suspected that the keel 

 of natalensis represents a mutation quite unconnected with the 

 smooth scale of hoplogaster. but careful examination of the latter 

 species led to the discovery of a very slight, but nevertheless dis- 

 tinct rudiment of a keel in the ventral scales of hoplogaster, 

 which at once suggests that the natalensis condition has been 

 arrived at through a series of minute stages and that the hoplo- 

 gaster and natalensis conditions will be found to grade. Similarly 

 though the ringhals has all its body scales sharply keeled, whilst 

 its generic allies the cobras have smooth scales, we cannot assume 

 that this is a mutation character, seeing that in other snakes such 

 as Causus or Leptodira all grades from strongly keeled scales to 

 smooth scales may be met with in the same genus, whilst the 

 same species may exhibit a wide range of variation in its keeling. 

 The genus Acontias, including our commonest blindworm. will 

 probably afford an interesting study in evolution, as dt has dift'er- 

 entiated into species which in certain localities are very distinct, 

 but in other places seem to merge. Acontias meleagris and A. 

 lineatns occur together in Little Namaqualand, where they seem 

 to be quite distinct species, the latter being easily recognised by its 

 much depressed and strongly projecting snout. At Port Eliza- 

 beth typical meleagris occurs, and along with it a form which is 

 recorded by systematists under the name of lineatus, but whilst 

 agreeing in all other respects with that species, it differs in the 

 form of the snout, therein resembling meleagris rather than 

 lineatus, and indeed it may be an aberrant juvenile form of 

 meleagris Whatever name we apply to it, this form may be 

 fairly regarded as intermediate between lineatus proper and 

 meleagris (juvenile) but such intermediates are not found appa- 

 rently in Namaqualand The large black blind worm Acontias 



