344 ESSAY ON CLASSIFICATION. 



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 dis- 

 tinctly, 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, 1 or upon the degree of superiority or inferi- 

 ority 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 M'LEAY. 



The great merit of the system of M'Leay 2 and in my 

 opinion it has no other claim to our consideration con- 

 sists in having called prominently the attention of natu- 

 ralists to the difference between two kinds of relationship 

 almost universally confounded before, affinity and ana- 

 logy. Analogy is shown to consist in the repetition 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 



1 Compare Chap. II, Sect. 3, p. 233. of the German physiophilosophers, 



2 1 have introduced the classifica- but on account of its general charac- 

 tion of M'Leay into this section, not ter, and because it is based upon an 

 because of any resemblance to those ideal view of the affinities of animals. 



