192 ESSAY ON CLASSIFICATION 



these organs are yet homologous as parts of the body of an Articulate. 

 This and similar cases may show how wide a field of investigation 

 lies before us in the study and discrimination of homological and 

 analogical forms. 



Generic analogies. As the generic characters are based upon pecu- 

 liarities of structure limited to some part or other of an animal, we 

 may expect to find the generic analogies reduced to a resemblance 

 of certain parts of the body and not extending to its general appear- 

 ance. For while genera, as members of a family, must exhibit the 

 same form, combined with the structural complication of their order, 

 it is obvious that if there is any generic analogy between animals of 

 different families their whole form may be widely different and the 

 complication of their structure exhibit entirely different combina- 

 tions, or be based upon different modes of execution, if they belong 

 to different classes, and even be constructed upon different plans of 

 structure if they belong to different branches; and yet seme of their 

 parts should be similar in some way or other, in order to present a 

 generic analogy. 



Now such generic analogies are rather frequent and may be traced 

 between animals of widely different families belonging to different 

 orders, nay, even to different classes and to different branches; for 

 instance, there is a marked generic analogy between the dentition 

 of the Insectivora, of the class of Mammalia, and that of the Chara- 

 cini of the class of Fishes, so also between some genera of the family 

 of Sparoids and those of the Chromids, between some genera of the 

 family of Insectivora and the Rodentia, and between some of the 

 family of Bombryces and of the Papiliones, etc. 



Specific analogies. If the characteristic features of species be truly 

 found in the relations which animals bear to the surrounding world 

 or to one another, and in the relative proportions of their parts and 

 their ornamentation, we cannot fail to find specific analogies result- 

 ing from these different aspects in animals belonging to different 

 genera, to different families, to different orders, and even to different 

 classes and branches. As far as they are aquatic, animals belonging to 

 different genera which number terrestrial species also have a certain 

 analogy with one another. All animals living in pairs or in flocks, or 

 isolated, may in this respect be considered as having an analogy to 

 one another, especially if they belong to genera in which different 



