Cii.vp. I. STRUCTURE AND GEOGRAPHICAL DISTRIBUTION. 39 



While all the representatives of the same genus are identical in .structure,' the 

 different species of one genus differ only in their size, in the proportions of their 

 parts, in their ornamentation, in their relations to the surrounding elements, etc. 

 The geographical range of these species varies so greatly, that it cannot afford in 

 itself a criterion for the di.stinction of species. It appears further, that while some 

 species which are scattered over very extensive areas, occupy disconnected parts of 

 that area, other species closely allied to one another and which are generally desig- 

 nated under the name of representative .species, occupy respectively such disconnected 

 sections of these areas. The question then arises, how these natural boundaries 

 assigned to every species are established. It is now generally believed that each 

 species had, in the beginning, some starting point, from which it has spread over 

 the whole range of the area it now occupies, and that this starting point is still 

 indicated by the prevalence or concentration of such species in some particular part 

 of its natural area, which, on that account, is called its centre of distribution or 

 centre of creation, while at its external limits the representatives of .such species thin 

 out, as it were, occurring more sparsely and sometimes in a reduced condition. 



It was a great progress in our science, when the more extensive and precise 

 knowledge of the geographical distribution of organized beings forced upon its 

 cultivators the conviction, that neither animals nor plants could have originated upon 

 one and the same spot upon the surface of the earth, and hence have spread more 

 and more widely until the whole globe became inhabited. It was really an immense 

 progress which freed science from the fetters of an old prejudice; for now we have 

 the facts of the case before us, it is really difficult to conceive how, Ijy assmning 

 such a gradual dissemination from one spot, the diversity which exists in every part 

 of the globe could ever have seemed to be exjilained. But even to grant distinct 

 centres of distribution for each species within their natural boundaries, is only to 

 meet the facts half way, as there are inninneraljlc relations between the animals and 

 plants which we find associated ever^^vhere, which mu.st be considered as primitive, 

 and cannot be the result of successive adaptation. And if this be so, it would 

 follow that all animals and plants have occupied, from the l)eginning, those natural 

 boundaries within which they stand to one another in such harmonious relations.^ 

 Pines have originated in foresis, heaths in heathers, grasses in prairies, bees in hive.s, 

 herrings in .schools, buffaloes in herds, men in nations!'' I see a striking proof that 

 this must have been the case in the circumstance, that representative species, which, 



^ See hereafter,- Cliap. II. Sect. .5. • Agassiz, (L..) The Diversity of Origin of the 



'' Agassiz, (L.,) Cieograi)iiical Distribution of Human Races, C'liristian Kxaininer. Boston, ISJO, 



Animals, Christian Examiner, lioston, 1850, 8vo. 8vo. (February.) 



(March). 



