84 THE VOYAGE OF H.M.S. CHALLENGER. 



artificial and in no way tenable. I quite agree with Jean Lamarck, who has entitled the 

 first chapter of his classical Philosophic Zoologique (1809) : — "Des parties de l'art dans 

 les productions de la nature " ; he has clearly proved that all our systematic categories, 

 classes and orders, no less than the genera and species, are artificial products of the human 

 mind, and that they all possess only a relative, not an absolute, character. The theory of 

 selection, given half a century afterwards by the immortal Charles Darwin, explains how 

 all these categories have arisen, and shows that natural classification can only be 

 phylogenetical, and that all apparently " good species " were originally " bad species." 



Special diligence has been displayed by Polejaeff in giving an absolute definition of 

 the category of genus. According to him, " generic unity serves as a firm basis, which 

 has been wanting in descriptive zoology since the mutability of species was actually 

 proved." 1 He regards " the generic character to be a character of sufficient constancy, 

 and together with this, allowing numerous modifications either in the direction of a 

 further development or in the direction of different variations."' 2 But may we not say 

 the same of the family ? the same of the species ? the same of the variety ? This 

 dogmatic definition, and also any other attempt to characterise any category of the 

 system by an absolute definition, are, in my opinion, quite untenable and worthless. I 

 think I have proved this in chapter xxiv. of my General Morphology. Genera are 

 artificial conceptions in the same way as species ; varieties are incipient species, species 

 incipient genera. 



Polejaeff gives in chapter ii. of his Report on the Keratosa a criticism of the genera, 

 and commences it with an enumeration of the three conditions which Nageli holds 

 indispensable for the absolute distinction of genera. 3 But what Nageli demands for 

 the allied species of one genus may be demanded for the genera of one family, the same 

 for the families of one order, the same for the varieties of one species. Polejaeff adopts 

 the opinion of Nageli, that "the existence of an absolute distinction of genera is 

 indispensable," 4 and he undertakes to give such an absolute distinction. In my opinion, 

 these genera are no more and no less artificial than all other genera. The history of 

 systematic classification shows us that the absolute distinction of genera is quite impossible, 

 and that the progress of one century has been sufficient to dissolve the definitions and 

 the conceptions of nearly all the older genera, and to replace them by a larger number of 

 smaller genera ; the latter, of course, must increase in the same degree as the specialisation 

 of our knowledge and the specification of minor morphological differences. 



Having stated that the first principles of classification employed by Polejaeff and by 

 myself are quite contrary to each other, and that we have adopted quite opposite 

 general views, it will be understood that as a natural consequence this diligent Russian 

 author severely attacks the less important parts of my Monograph of Calcispongiae. 



1 Zool. Chall. Exp., pt. xxxi. p. 82. - Narr. Chall. Exp., vol. i. p. 644. 



3 Loc. cit., p. 21. 4 Narr. Chall. Exp., vol. i. p. 645. 



