i26 HISfORY OF ZOOLOGY. 



Separation of the Artificial and Natural Methods in Tchthyolor/y. 

 It has already been said that all so-called artificial methods of classifi 

 cation must be natural, at least as to the narrowest members of the 

 system; thus the artificial Linnaean method is natural as to species, 

 and even as to genera. And on the other hand, all proposed natural 

 methods, so long as they remain unmodified, are artificial as to theii 

 characteristic marks. Thus a Natural Method is an attempt to pro- 

 vide positive and distinct characters for the wider as well as for the 

 narrower natural groups. These considerations are applicable to 

 zoology as well as to botany. But the question, how we know natu- 

 ral groups before we find marks for them, was, in botany, as we have 

 seen, susceptible only of vague and obscure answers : the mind forms 

 them, it was said, by taking the aggregate of all the characters ; or 

 by establishing a subordination of characters. And each of these 

 answers had its difficulty, of which the solution appeared to be, that 

 in attempting to form natural orders we are really guided by a latent 

 undeveloped estimate of physiological relations. Now this principle, 

 which was so dimly seen in the study of vegetables, shines out with much 

 greater clearness when we come to the study of animals, in which the 

 physiological relations of the parts are so manifest that they cannot 

 be overlooked, and have so strong an attraction for our curiosity that 

 we cannot help having our judgments influenced by them. Hence the 

 superiority of natural systems in zoology would probably be far more 

 generally allowed than in botany ; and no arrangement of animals 

 which, in a large number of instances, violated strong and clear natu- 

 ral affinities, would be tolerated because it answered the purpose of 

 enabling us easily to find the name and place of the animal in the 

 artificial system. Every system of zoological arrangement may be 

 supposed to aspire to fee a natural system. But according to the 

 various habits of the minds of systematizers, this object was pursued 

 more or less steadily and successfully ; and these differences came 

 more and more into view with the increase of knowledge and the mul- 

 tiplication of attempts. 



Bloch, whose ichthyological labors have been mentioned, followed 

 in his great work the method of Linnaeus. But towards the end of 

 his life he had prepared a general system, founded upon one single 

 numerical principle ; the number of fins ; just as the sexual system 

 of Linnaeus is 'founded upon the number of stamina ; and he made his 

 subdivisions according to the position of the ventral and pectoral fins 

 the same character which Linnaeus had employed for his priman 



