102 TERMINOLOGY AND CLASSIFICATION OF DIATOMS. 



we shall gradually be able to determine the variations of the principal forms 

 which are to be found around us. It will be no inconsiderable service 

 that Dr. Miquel will thus have rendered to diatomology by having 

 thus suddenly developed a new method, which will enable diatomologists 

 to confidently pursue a series of studies, which cannot but lead to results 

 of the utmost importance in the future. 



Whilst I have endeavoured to fall in with these recent ideas, and 

 as this work is especially intended for beginners, I have preferred to use 

 " Species " in its widest sense, and I have adopted a small number of 

 principal type-forms, to which I have referred secondary type-forms. 

 This will prevent the beginner from losing himself in a complicated 

 labyrinth of forms, while those who do not share this view have only 

 to raise my varieties to the rank of species. 



The preceding lines were written before I received from Mr. C. Naudin 

 his work on " kindred species " (*). I am pleased to see that this learned 

 botanist, who has had such prolonged experience and is so competent 

 an authority on the subject, has arrived by the cultivation of Phanerogamia at 

 the same conclusion as myself. <: Any objective definition of species," writes 

 Mr. Naudin, "is impossible, and one must either be content with the 

 arbitrary definition of Linnseus and his successors or admit with me that 

 Species, Race, and Variety are purely rational categories, which the fancy 

 of each person modifies according to the impression that he receives of 

 any object and this impression varies in each individual, and even in the 

 same individual it will depend upon that mental state in which he happens to 

 find himself. . . ." ' ; Nomenclature," says the author a little further on, 

 " should know when to stop on the downward course of subdividing, 

 the exaggeration of which would produce the gravest consequences. It 

 is first necessary to settle and fix amicably the limits at which it would 

 be convenient to stop, so as not to overcharge with terms sciences already too 

 much encumbered, and which, without this prudent check, would gradually 

 become quite unapproachable." " . . . I know of certain authors whose 

 writings would seem to shew that specific subdivision was quite a mania with 

 them, and it is quite necessary to point out the mal-treatment that certain 

 good Linnaean species have suffered at their hands : for before they had been 

 cut about in this way they were perfectly recognizable, but since this so-called 

 improvement these authors have in their books made quite an inexplicable 

 magma of them. What benefit have these authors rendered to science? 



( T ) Les especes atfines et la theorie de Evolution par Ch. Naudin de l'Institut. Paris, 

 Bailliere et fils. 



