Dr L. Mandl on the Scales of Fishes. 123 



to such characters as these, there is still another point most 

 commonly overlooked by naturalists, on which we wish to say 

 a few words. 



Any property whatever, which constitutes a natural charac- 

 ter, may vary in different degrees, and thus constitute in its 

 successive changes a continuous series. Relations unite all the 

 members of this series ; no one is separated from another by 

 a real difference, and each member of this series may be re- 

 placed by another of the same series, without changing the 

 nature of the being. Thus, for example, white and red colours, 

 with ail their variations, may be found in roses without dis- 

 tinction, and yet no new species be created. All the shades 

 between white and red, form in this case, then, a natural series, 

 the members of which may be substituted for each other with- 

 out changing the nature of the rose. 



Professor Mobs has made a very successful application of 

 these principles to mineralogy, or, to speak more properly, these 

 ideas of natural characters and the series they constitute, owe 

 their origin to this distinguished philosopher. The creation 

 of the systems of crystallization, such, for example, as the tes- 

 sular, rhomboidal, pyramidal systems, &c., gave birth to as 

 many natural series, containing a multitude of members, all 

 of which may be substituted for each other, but which are 

 in themselves essentially separated, and cannot be confound- 

 ed. Thus it is of little importance, for the determination 

 of a species, whether the mineral be crystallized under the 

 form of a cube, or any other derived from that ; but never 

 can it present, for example, a pyramidal form, for there is no 

 transition between a cube and a pyramid. 



It is only characters, then, which distinguish series, and 

 which admit of no transition, that can ailthorize us to establish 

 distinctions between beings, and create new species. When- 

 ever there is a passage between the characters of a new in- 

 dividual and those of one previously known, we cannot make 

 a real division. Unhappily the neglect, or perhaps the igno- 

 rance, of these principles, has led many naturalists to create a 

 multitude of species founded on distinctions ({uite futile, and 

 (if I may be pardoned the expression) altogether foolish, pro- 

 ducing an incumbrance of new species sufficient to cause 

 disgust for the study of natural history. 



