182 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



formed by the Cats, Hyenas, Dogs, Viverridae, and Weasels, 

 are much more unlike one another, and so form a less con- 

 solidated sphere than the Ruminants. So much the more nume- 

 rous and more nearly approximated to other families are their 

 transitional forms, by which in the Potto they approach the 

 Quadrumana ; in the Insectivora, the Rodents ; in the Fish 

 the Otter, the Seal and the Walrus, the Cetacea ; in the Marsu- 

 pialia, the Monotremata ; and these transitional forms are upon 

 the whole far poorer in individuals than the aberrant forms of 

 more narrowly limited families. The Rodents present nearly 

 the same peculiarities. Among the proper quadrupeds the least 

 consolidated sphere is that of the Pachydermata, which, however, 

 in relation to the small number of those forms which can be 

 considered central, has many aberrant members, the Daman, 

 the Elephant, the Solidungulata ; and in the ancient world there 

 were yet more. Among Birds the transitional forms are more 

 solitary genera, the Ostriches and Cassowaries, which under the 

 influence of the more consolidated centre are only single mu- 

 tually divergent groups. Among the Mammalia, where even the 

 central forms are not so closely arranged, the transitional or atmo- 

 spheric groups themselves compose considerable spheres. The 

 Quadrumana, a transition to Man, form a numerous order, whose 

 centre is constituted by the true Apes ; while the Makis, the 

 transition to the proper quadrupeds, form single small scattered 

 families. Not so the Bats, for which the genera Pteropus, and 

 still more Galeopithecus, are transitional forms. Most distant 

 from the centre of the proper quadrupeds are the Monotremata ; 

 and in accordance with this we find that they contain but few 

 genera, among which considerable differences exist, and that even 

 the species are represented by but few individuals. If we glance 

 at the Amphibia, we find that the members of the most aber- 

 rant group, the Sirenidae, are not only more dissimilar from one 

 another, than, for example, all the tail-less Batrachia which oc- 

 cupy the centre are, but that their occurrence is limited to a 

 few places. 



Do not these considerations show that the Idea of animal or- 

 ganization does not vary at equal intervals, but, as we observed 

 above, is realized in certain principal forms which again break 

 up into variations of a lower grade, in such a manner that the 



