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Cii. XXXIV.] 



MEANING OF THE TERM 'SPECIES. 



245 



This branch of our enquiry naturally divides itself into two 



parts : 



nieaninp-s which have 



term 



from 



origin the same, only varying within certain fixed and de- 



modified 



m 



the course of a long series of generations. This will lead 



animal 



inanimate 



ing and temporary conditions in 

 worlds and the consequent ex- 

 tinction of species one after the other^ and the manner in 

 which the places left vacant may be supplied by new animals 

 and plants better fitted for the new conditions. 



may 



some 



individuals of certain species may occasionally become fossil. 



manner as to form 



may 



ages as monuments of the state of the living world at the 

 time when they became fossil. 



Before we can advance a step in our enquiry, we must 



minds as to the meanm 



we attach to the term ' species.' This is even more necessary 

 in geology than in the ordinary studies of the naturalist ; for 



modifiability 



may 



as if the specific character were constant, because they confine 

 their observations to a brief period of time. Just as the 

 astronomer, in constructing his maps of the heavens, may 

 proceed century after century as if the apparent places of the 



remained absolutelv the same 



motion 



so, it is said, in the organic world, the stability of a species 

 may be taken as absolute, if we do not extend our views 

 beyond the narrow period of human history ; but let a suffi- 

 cient number of centuries elapse, to allow of important 

 revolutions in climate, physical geography, and other cir- 

 cumstances, and the characters, say they, of the descendants 



