'2SO ESSAY ON CLASSIFICATION. 



cific analogy. The pattern of colouration may also exhibit 

 specific analogy, as, for instance, in the transverse bands 

 of the tiger when compared to the Quagga, in the spots 

 of the leopard and the Giraffe, which is so striking as to 

 have 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 examples 

 may suffice to call attention to the subject, and to lead 

 hereafter to a more careful investigation of the different 

 categories 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, whether 

 extensive or limited, are strictly confined within groups 

 of the same kind, it is evident that unless any feature 

 observed in any animal be common to all the representa- 

 tives of the group in which it occurs, we shall have good 

 reason 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 of 

 Vertebrates, any structure in the longitudinal axis of an 

 animal which is not structurally identical with the dorsal 

 cord* cannot be homologous with it, but must be some- 

 thing only analogous to it; for instance, the medial stripe 

 which appears during the early development of the em- 

 bryo of the earlier Crustacea. For the farther progress 

 of the formation of the backbone, we trace the formation 

 of arches below as well as above the dorsal cord, while in 

 Crustacea, there is a similar development only on one 

 side. We are therefore compelled to consider the solid 

 arches 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, 

 a.s iii Vertebrates, but all the other viscera besides. The 



