196 SPECIES NOT 



cessary for its growth the soil, temperature, 

 moisture, and light. Assuming the truth, also, 

 of special centres of creation, it by no means 

 follows that Mr. Darwin's views, as to the effect 

 of barriers upon migration, should be the real 

 cause of the difference between the faunae of two 

 countries, as South and Central America, or the 

 western and eastern shores of the Pacific. If it 

 were so, how are we to account for such facts 

 as the following? "Indeed I am inclined to 

 believe that there are very few South American 

 birds, except in the more widely-diffused accipitres, 

 grallrc, and anseres, which are really to be met 

 with in Mexico and Central America." (Sclater, 

 in Proceedings of Zoological Society, Part 1, 1859, 

 page 45.) Here are no barriers, for the land 

 is continuous between one country and another. 

 But this difference of species on different parts 

 of the world, is by no means universal. Pro- 

 fessor Asa Gray has recently pointed out, in a 

 paper read before the American Scientific Asso- 

 ciation, on the similarity of the plants of north- 

 eastern Asia and those of the eastern portion of 

 North America, that, "In many cases, there is 

 not only similarity, but even identity of species." 

 Among instances of identity he mentions gentian, 

 noble-bush, poison ivy, cranberry, and others, 

 which are of the same species on both conti- 

 nents, and it is probable that further researches 

 will disclose additional instances. Even where 

 there is a difference in species, there is generally 

 a remarkable similarity in many of the genera 



