LEADING GROUPS OF EXISTING SYSTEMS 193 



species bear these different relations to one another. But it is in the 

 proportions of the parts to one another in the species of different 

 genera belonging to the same family or even to different families of 

 the same class, and in the ornamentation of their surface, that we 

 observe the most numerous specific analogies. Reference has already 

 been made to the specific homologies resulting from the relative 

 length of the head, the neck, the tail, etc. But there is a specific anal- 

 ogy only between the Zerda, a species of dog found in the interior 

 of Africa, which is characterized by the extraordinary length of its 

 ears, and those species of hare which live also in the desert and have 

 much larger and longer ears than those inhabiting the woods and 

 marshes. This analogy is no doubt owing to the fact that under the 

 conditions in which these animals are placed they require a keener 

 perception of sound, and yet they belong to different orders, though 

 of the same class. This is therefore a specific analogy. The pattern 

 of coloration 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 analogies through- 

 out the Animal Kingdom, these few examples may suffice to call at- 

 tention to the subject and to lead hereafter to a more careful investi- 

 gation of the different categories of analogy. A few more remarks 

 may, however, find a place here to show how to distinguish analogical 

 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 representatives of the group in which it occurs, we shall 

 have good reason to suspect that it is not based upon strict homology, 

 but rather belongs to some category of analogy. If, for instance, the 

 dorsal cord is a fimdamental 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 ap- 

 pears during the early development of the embryo 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 



