216 ESSAY ON CLASSIFICATION. Part I. 



Instead of considering the orders as founded upon a repetition of the characters 

 of higher groups, as Oken would have it, Fitzinger adopts series, as founded upon 

 that idea, and subdivides them further into orders, as above. These series, however, 

 have still less reference to the systems of organs, which they are said to represent, 

 than either the classes or the higher divisions of the animal kingdom. In these 

 attempts to arrange minor groups of animals into natural series, no one can fail 

 to perceive an eftbrt to adapt the frames of our systems to the impression we 

 receive from a careful examination of the natural relations of organized beings. 

 Everywhere we notice such series; sometimes extending only over groups of species, 

 at other times embracing many genera, entire families, nay, extending frequently to 

 several families. Even the classes of the same branch may exhibit more or less 

 distinctly such a serial gradation. But I have failed, thus far, to discover the 

 principle to which such relations may be referred, as far as they do not rest upon 

 complication of structure,^ or upon the degree of superiority or inferiority of the 

 features upon which the different kinds of groups are themselves founded. Analogy 

 plays also into the series, but before the categories of analogy have been as 

 carefully scrutinized as those of affinity, it is impossible to say within what limits 

 this takes place. 



CLASSIFICATION OF McLEAY. 



The great mei'it of the system of McLeay,^ and in my opinion it has no other 

 claim to our consideration, consists in having called prominently the attention of 

 naturalists to the difference between two kinds of relationship, almost universally 

 confounded before : affinity and analogy. Analogy is shown to consist in the repeti- 

 tion of similar features in groups otherwise remote, as far as their anatomical 

 characters are concerned, whilst affinity is based upon similarity in the structural 

 relations. On account of the similarity of their locomotion. Bats, for instance, may 

 be considered as analogous to Birds ; Whales are analogous to Fishes on account 

 of the similarity of their form and their aquatic mode of life ; whilst both Bats 

 and Whales are allied to one another and to other Mammalia on account of the 

 identity of the most characteristic features of their structure. This important dis- 

 tinction cannot fail to lead to interesting results. Thus far, however, it has only 

 produced fanciful comparisons from those who first traced it out. It is assumed, 

 for instance, by McLeay, that all animals of one group must be analogous to 



^ Compare Chap. II., Sect. 3, p. 153. those of the German physiophilosophers, but on 



^ I have introduced the classification of McLeay account of its general character, and because it is 

 in this section, not because of any resemblance to based upon an ideal view of the affinities of animals. 



