Chap. IL FAMILIES. 155 



Fishes, and Sensual Fishes, and so also in the classes of Reptiles, Birds, and 

 Mammalia.^ 



I have entered into so many details upon these vagaries of the distinguished 

 German pliilosopher, because these views, however crude, have undoubtedly been 

 suggested by a feature of the animal kingdom, which has thus far been too little 

 studied: I mean the analogies which exist among animals, besides their true affinities, 

 and which cross and blend, under modific^ations of strictly homological structures, 

 other characters wliich are only analogical. But it seems to me that the subject 

 of analogies is too little known, the facts bearmg upon this kind of relationship 

 being still too obscure, to be taken as the basis of such important groups in the 

 animal kingdom as the orders are, and 1 would insist upon considering the comjilica- 

 tion or gradation of structure as the feature which should regulate their limitation, 

 if under order we are to understand natiu-al groups expressing the rank, the relative 

 standing, the superiority or inferiority of animals in their respective classes. Of 

 course, groups thus characterized cannot be considered as mere modifications of the 

 classes, being founded upon a special category of features. 



SECTION IV 



FAMILIES. 



Nothing is more indefinite than the idea of fonn, as applied by systematic 

 writers, in characterizing animals. Here, it means a system of the most difl'erent 

 figures having a common character, as, for instance, when it is said of Zoopln-tes 

 that they have a radiated form ; there, it indicates any outline which circumscribes 

 the body of animals, when, for instance, animal forms are alluded to in general, 

 instead of designating them simply as animals ; here, again, it means the special 

 figure of some individual species. Tliere i.s in fact no group of the animal king- 

 dom, however extensive or however limited, from the branches down to the species, 

 in which the fonn is not occasionally alluded to as characterLstic. Speaking of Articu- 

 lates, C. K v. Baer characterizes them as the type with elongated forms ; Mollusks 

 are to him the type with massive forms ; Radiata"? that with peripheric symmetry ; 

 Vertebrates that with double symmetry, evidently taking their fonn in its widest 

 sense as expressing the most general relations of the different dimensions of the 



' See fiirtluT (levelopincnts upon this subject in Xjiturgeschichte. vol. 4, p. 582. Compare also the 



Oken's Naturpliilosophic, and in his Allgcnieine following chapter. 



