152 ESSAY ON CLASSIFICATION. Part I. 



noids among Acaloplis; the Crinoids, Asterioids, Echiuoids, and HolothnriiB among 

 Echinodei'ms ; the Bryozoa, Brachiopods, Tunica ta, LameUibranchiata among Acephala ; 

 the Branchifera and Pulmonata among Gasteropods ; the Ophidians, the Saurians, 

 .and the Chelonians among Reptiles ; the Ichthyoids and the Anoura among Amphi- 

 bians, etc. 



Having shown in the pi'eceding paragraph that classes rank next to branches, 

 it would be proper I should show here that orders are natural groups which stand 

 above families in their respective classes ; but for obvious reasons I have deferred 

 this discussion to the following paragraph, which relates to fxmilies, as it will be 

 easier for me to show what is the respective relation of these two kinds of groups 

 after their special character has been duly considered. 



From the preceding remarks respecting orders it might be inferred that I deny 

 •all gradation among all other groups, or that I assume that orders constitute neces- 

 sarily one simple sei'ies in each class. Far from asserting any such thing, I hold 

 on the contrary, that neither is necessarily the case. But to explain fully my 

 •views upon this point, I must introduce here some other considerations. It will 

 be obvious, from what has already been said, (and the fm'ther illustration of this 

 subject will only go to show to what extent this is true,) that there exists an 

 janquestionable hierarchy between the different kinds of groups admitted in our 

 systems, based upon the different kinds of relationship observed among animals, 

 that branches are the most comprehensive divisions, including each several classes, 

 that orders are subdivisions of the classes, families subdivisions of orders, genera 

 subdivisions of families, and species subdivisions of the genera ; but not in the 

 sense that each type should necessarily include the same number of classes, nor 

 even necessarily several classes, as this must depend upon the manner in which 

 the type is carried out. A class, again, might contain no orders,^ if its represent- 

 atives presented no different degrees characterized by the greater or less compli- 

 cation of their structure ; or it may contain many, or few, as these gradations are 

 more or less numerous and well marked ; but as the representatives of any and 

 every class have of necessity a definite form, each class must contain at least one 

 family, or many families, indeed, as many as there are systems of fomis under 

 which its representatives may be combined, if form can be shown to be charac- 

 teristic of families. The same is the case with genera and species; and nothing 

 is more remote from the truth than the idea that a genus is better defined in 

 proportion as it contains a greater number of species, or that it may be necessary 

 to know several species of a genus before its existence can be fully ascertained. 

 A genus may be more satisfactorily characterized, its peculiarity more fully ascer- 



» See Clmp. I. Sect. 1. 



