SPECIES AND VARIETY. 181 



avowedly Colonel Smith's ; but, in justice to the latter 

 gentleman, it must be added, that the disquisitions on 

 the circular succession of forms, and the analogical rela- 

 tions, are entirely Mr. Swainson's. 



ON SPECIES AND VARIETY. 



What constitutes a species ? And how far do the 

 limits of varieties extend ? Cuvier, who is, perhaps, the 

 best authority we can have upon this subject, in defining 

 a species, says : A species comprehends all the indivi- 

 duals which descend from each other or from a common 

 parentage, and those which resemble them as much as they 

 do each other. Thus, the different races which they have 

 generated from them are considered as varieties but of 

 one species. Our observations, therefore, respecting the 

 differences between the ancestors and the descendants, 

 are the only rules by which we can judge on this subject; 

 all other considerations being merely hypothetical, and 

 destitute of proof. Taking the word variety in this 

 limited sense, we observe that the differences which con- 

 stitute this variety depend upon determinate circum- 

 stances, and that their extent increases in proportion to 

 the intensity of the circumstances which occasion them. 



Upon these principles it is obvious, that the most 

 superficial characters are the most variable. Thus colour 

 depends much upon light ; thickness of hair upon heat ; 



