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ESSAY ON CLASSIFICATION.

relations of organized beings. Everywhere we notice suchseries; sometimes extending only over groups of species,at other times embracing many genera, entire families,—nay, extending frequently to several families. Even theclasses of the same branch may exhibit, more or less dis-tinctly, such a serial gradation. But I have failed, thusfar, to discover the principle to which such relations maybe referred, as far as they do not rest upon complicationof structure , 1 or upon the degree of superiority or inferi-ority of the features upon which the different kinds ofgroups are themselves founded. Analogy plays also intothe series; but before the categories of analogy have beenas carefully scrutinized as those of affinity, it is impossibleto say within what limits this takes place.

CLASSIFICATION OF m’lEAY.

The great merit of the system of M’Leay 2 —and in myopinion 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 relationshipalmost universally confounded before ,—affinity and ana-logy. Analogy is shown to consist in the repetition ofsimilar features in groups otherwise remote, as far as theiranatomical characters are concerned, whilst affinity isbased upon similarity in the structural relations. Onaccount of the similarity of their locomotion, Bats, forinstance, may be considered as analogous to Birds; Whalesare analogous to Fishes on account of the similarity oftheir form and their aquatic mode of life; whilst both

1 Compare Chap. II, Sect. 3, p.233. of the German physiophilosophers,3 1 have introduced the classifica- but on account of its general charae-tion of M’Leay into this section, not ter, and because it is based upon anbecause of any resemblance to those ideal view of the affinities of animals.