4 ESSAY ON CLASSIFICATION. 



is a matter of consequence, whether genera are circum- 

 scribed in our systematic works within these or those 

 limits ; whether families inclose a wider or more contracted 

 range of genera ; whether such or such orders are admitted 

 in a class, and what are the natural boundaries of classes ; 

 as well as how the classes themselves are related to one 

 another, and whether or not all these groups are considered 

 as resting upon the same foundation in nature. 



Without venturing here upon an analysis of the various 

 systems of Zoology, the prominent features of which are 

 sufficiently exemplified for my purpose by the systems of 

 Linnaeus and Cuvier, 1 which must be familiar to every 

 student of Natural History it is certainly a seasonable 

 question to ask, whether the animal kingdom exhibits only 

 those few subdivisions into orders and genera, which the 

 Lhmaean system indicates, or whether the classes differ 

 among themselves to the extent which the system of 

 Cuvier would lead .us to suppose. Or is, after all, this 

 complicated structure of classification merely an ingenious 

 human invention which every one may shape, as he 

 pleases, to suit himself? When we remember that all 

 works on Natural History admit some system or other of 

 this kind, it is certainly an aim worthy of a true naturalist, 

 to ascertain what is the real meaning of all these divisions. 



Embryology, moreover, forces the inquiry upon us at 

 every step, as it is impossible to establish precise compa- 

 risons between the different stages of growth of young 

 animals of any higher group, and the permanent charac- 

 ters of full-grown individuals of other types, without first 

 ascertaining what is the value of the divisions with which 

 we may have to compare embryos. My studies in this 

 department have led me for many years to pay the most 



1 riompare Chap. III. 



