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ESSAY ON CLASSIFICATION.

cific analogy. The pattern of colouration may also exhibitspecific analogy, as, for instance, in the transverse bandsof the tiger when compared to the Quagga, in the spotsof the leopard and the Giraffe , which is so striking as tohave suggested the name of the latter, Camelo-pardalis.

As it is not my intention here to trace all these analo-gies throughout the Animal Kingdom, these few examplesmay suffice to call attention to the subject, and to leadhereafter to a more careful investigation of the differentcategories of analogy. A few more remarks may, how-ever, find a place here to show how to distinguish analo-gical from homological features. As homologies, whetherextensive or limited, are strictly confined within groupsof the same kind, it is evident that unless any featureobserved in any animal be common to all the representa-tives of the group in which it occurs, we shall have goodreason to suspect that it is not based upon strict homo-logy, but rather belongs to some category of analogy. If,for instance, the dorsal cord is a fundamental feature ofVertebrates , any structure in the longitudinal axis of ananimal which is not structurally identical with the dorsalcord cannot be homologous with it, but must be some-thing only analogous to it; for instance, the medial stripewhich appears during the early development of the em-bryo of the earlier Crustacea , For the farther progressof the formation of the backbone, we trace the formationof arches below as well as above the dorsal cord, while inCrustacea , there is a similar development only on oneside. We are therefore compelled to consider the solidarches of Crustacea only as analogous structures to Ver­ tebrae and not as homologous with them, the more so,since these arches enclose not only the nervous system,as in Vertebrates , but all the other viscera besides. The