K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 181 



viduals, and the more extensively scattered over the earth's 

 surface, the more closely they are connected with the centre of 

 a sphere of modification. 



What has been said may be made more intelligible by exam- 

 ples. I choose them from among the Vertebrata, and, indeed, 

 from the higher classes, because our acquaintance with these is 

 least defective. The Mammalia differ so much from one an- 

 other, that without anatomical examination they could hardly 

 be recognised as modifications of one principal form. Their 

 centre is evidently formed by the proper quadrupeds, while the 

 climbers (Quadrumana), the fliers (Cheiroptera), the swimmers 

 (Cetacea), and lastly the Monotremata, represent the atmosphere, 

 or the aberrant forms. The proper quadrupeds even present 

 considerable differences from one another ; still more do the 

 peripheral forms differ from one another and from the central 

 forms. They considerably approach other principal forms, with- 

 out however truly passing into them ; for the organization of 

 the most aberrant forms, the Ornithorhynchus and the Whale, 

 is still so far removed from that of a true fish or amphibian, 

 that we can decide with certainty to which class they belong. It 

 is otherwise with Birds. All the orders are so similar in their 

 essential relations, that we find them as it were crowded 

 round the centre, and only the Ostrich with a few other birds 

 can be regarded as the peripheral members of this very con- 

 densed sphere. These peripheral members again do not de- 

 viate so far from the principal forms, but that the hastiest 

 inspection is sufficient to leave no doubt on the mind, whether 

 they are beasts or birds. Enclosed within these narrow bounds, 

 the number of Birds is yet at least six times as great as that of 

 the Mammalia. The peripheral forms among Birds are to the 

 central forms, hardly in the proportion of 1 to 1000 : in the 

 Mammalia they form more than one-fourth (!) of the whole. If 

 we turn to the subordinate spheres, we find in the centre of the 

 Mammalia a few families whose normal genera are very similar 

 to one another, as the Ruminants. Here the number of the 

 peripheral forms (the hornless Ruminants) is not only small, but 

 they are likewise few and scattered in the world (Camels are 

 multiplied only by human aid), in comparison with the herds of 

 Antelopes, Deer, and Oxen. The Carnivora, whose centre is 



