In dealing with the coloration, we have first to distinguish between the colour and the markings. The former is very often highly variable among snakes of the same species, to say nothing of the changes which may take place with age or with the condition of the individuals, whether before or after exuviation; it is not unusual to find among specimens from the same locality a great range of variation, from greyish-white to brown, or red, or black, as, for instance, in our Common Viper. The latter afford more important characters, and often furnish valuable indications for the distinction of species; but even the disposition of the markings is subject to great individual variations, more likely to mislead than to help the inexperienced student in the discrimination of species. It is therefore always advisable to resort in the first instance to structural characters for the purpose of specific identification, and to fall back on coloration only as a means of confirmation. If we were to be guided by colour and markings alone, how could we believe that an adult four-lined _Coluber quatuorlineatus_ is of the same species as the handsomely spotted _Coluber sauromates_; and yet, if we compare the young of these two snakes we find them to be absolutely identical in their markings, and, in the absence of any structural differences, we are forced to conclude that they only represent two forms of the same species, of which the latter is the more primitive. It is nevertheless a fact that, with a few exceptions, the markings, however variable they may be, are reducible to certain fundamental patterns to which the innumerable variations may be traced back, and their derivation followed and scientifically explained. Let us consider, for instance, another species of _Coluber_, highly variable in its markings: _C. leopardinus_, of which the typical form, so called from having been the first described and named, is not by any means to be regarded as the most primitive.