342 ^'HE GEOLOGIST, 



and vegetable kingdoms are constructed, and wliicli have been 

 selected bv natm-alists as the principles on whicb to groimd those 

 arbitrarv divisions and snb-di^-isions of scientific arrangement so 

 necessai^ for facilitating the acquirement of knowledge and for the 

 progi'ess of investigation. 



All animated or li^-ing things belong to one of two markedly dis- 

 tinct gi'oups — the animal or vegetable ; hence in scientific nomcn- 

 clatm-e the gTcatest distinctions are given to these thoronghlj 

 decided di^-isions, and they are consequently termed l-tngdonis. 

 Takino' either plants or animals it is apparent that of either we have 

 many sorts, and also that these sorts ai^e evidently constructed on 

 different plans, as for example seaweeds and trees, insects, Crustacea, 

 starfish, shells, qnadi'iipeds : hence we have principal di^-isions into 

 ,Q?'7/-/,;/,,/J,,,;,>\ d'ASses, and orders. Taking the members of any one 

 of these divisions, we find that, thongh there may be a common 

 resemblance on the whole, yet the tj-pical form, npon which all of 

 them are more or less constrncted, is nevertheless variously modi- 

 fied, and that nmnerons fonns, although subservient to the type, are 

 still modelled more dii^ectly upon some certain deviation or pecu- 

 Karity. For example, the class Mammalia has the characteristic 

 features of the Tertebrata in the possession of an internal bony 

 skeleton, consisting of a cranium, vertebral column, and two fore 

 and two hind limbs for terrestrial locomotion. But how distinctl}^ is 

 this vertebrate tyjje modified to suit the particular exigencies, habits, 

 and conditions of other vertebrate classes, such as fish, reptiles, 

 bhds, whales, man. Each of these classes again displays many dis- 

 tinctive modifications, as, for example, the eagle and the sparrow, 

 the hen-ing and the shark ; hence arise other subdivisions or orders, 

 and these again exhibit subservient modifications, as for instance the 

 eagle and the hawk. Those which have thus a gTeat resemblance 

 for each other are included in one f ami! ij, and are distinguished from 

 each other by a generic name, or in other words each family is made 

 up of difi'erent sorts or genera. These again are susceptible of divi- 

 sion by individual or special characters, whence the denomination of 

 species, the still minor variations of which — brought about by 

 difference of existence, physical conditions, or local cu'cmnstances — 

 arc indicated bv the term varipties. 



