LEADING GROUPS OF EXISTING SYSTEMS 177 



plan of structure of their respective type in a special manner, carried 

 out with special means and in special ways. 



As representatives of Branches these same individuals are all organ- 

 ized upon a distinct plan, differing from the plan of other types. 



Individuals then are the bearers, for the time being, not only of 

 specific characteristics, but of all the natural features in which ani- 

 mal life is displayed in all its diversity. 



Viewing individuals in this light, they resume all their dignity; 

 they are no longer absorbed in the species to be forever its represent- 

 atives, without ever being anything for themselves. On the contrary, 

 it becomes plain, from this point of view, that the individual is the 

 worthy bearer, for the time being, of all the riches of nature's wealth 

 of life. This view further teaches us how we may investigate, not only 

 the species in the individual, but the genus also, the family, the order, 

 the class, the branch, as indeed naturalists have at all times proved 

 in practice whilst denying the possibility of it in theory. 



Having thus cleared the field of what does not belong therein, it 

 now remains for me to show what in reality constitutes species, and 

 how they may be distinguished with precision within their natural 

 limits. 



If we would not exclude from the characteristics of species any 

 feature which is essential to it, nor force into it any one which is not 

 so, we must first acknowledge that it is one of the characters of spe- 

 cies to belong to a given period in the history of our globe, and to 

 hold definite relations to the physical conditions then prevailing and 

 to animals and plants then existing. These relations are manifold 

 and are exhibited: 1st, in the geographical range natural to any spe- 

 cies, as well as in its capability of being acclimated in countries where 

 it is not primitively found; 2d, in the connection in which they stand 

 to the elements around them, when they inhabit either the water, or 

 the land, deep seas, brooks, rivers and lakes, shoals, flat, sandy, muddy, 

 or rocky coasts, limestone banks, coral reefs, swamps, meadows, fields, 

 dry lands, salt deserts, sandy deserts, moist land, forests, shady groves, 

 sunny hills, low regions, plains, prairies, high table-lands, mountain 

 peaks, or the frozen barrens of the Arctics, etc.; 3d, in their depend- 

 ence upon this or that kind of food for their sustenance; 4th, in the 

 duration of their life; 5th, in the mode of their association with one 



