74 
DR. W. KOWALEYSKY ON THE 
And these last, as we shall presently see, being better adapted to altered conditions of 
life, got the upper hand, multiplied largely in specific and generic forms, and peopled the 
earth with their successors, while Anoplotherium and Xiphodon died away without leaving 
any*. In this inflexibility and rigidity of organization, in this inability to alter it as 
completely as the competing genera were able to do, lay perhaps one of the causes of the 
extinction of some genera and their replacement by others. All that I attempt here is 
to show in what peculiarities of structure this rigidity of some genera and pliancy of 
others consisted. I do not wish to put this as the only cause, but as one of the many 
still unknown causes which led to the extinction of so many animals that preceded the 
present population of the earth. 
I have adduced here only such cases as are known and described ; but having carefully 
examined large collections of bones from the Eocene and Miocene deposits, I have been 
struck with the recurrence of similar facts. Trying to reconstruct the extremities of some 
Paridigitata of the Lower Eocene from Mauremont and Egerkingen, and of Miocene forms 
from Rochette, I could distinctly perceive that all genera which have left no direct succes- 
sors, and which are entirely extinct, present the same rigidity and persistence of the 
typical relations ; on the contrary, those which have representatives in the living creation, 
their direct successors, exhibit much more pliancy and much better adaptation to altered 
circumstances of locomotion, along with the reduction in the number of digits. 
Before proceeding to consider the two remaining groups of Paridigitata, the 
Ruminantia and the Suina, we may draw the attention of the reader to the fact 
that these two groups of Paridigitata are the only onesf which now people the 
earth ; there is no greater diversity than this ; and every living Paridigitate (if we 
except the Hippopotamus) is always clearly a ruminant (including the Tragulidae and 
Camelidae) or a Sus. How striking is this poorness of different types if we compare it 
with the rich and diversified forms presented by the recent Carnivora or Rodentia. The 
extreme diversity of generic forms and specific modifications, coupled with the enormous 
range of distribution of living Paridigitata, produces a false impression of the diver- 
sity presented by this order ; but in reality there is no such diversity, and all the extremely 
rich assemblage of Paridigitate Ungulates that people the earth in our time are only the 
result of the modification of two typical forms, the Suina and the Ruminantia. The 
latter term is a very objectionable one, as the faculty of rumination has nothing to do 
with the skeleton, and in reality it would be no wonder if some of the Imparidigitates 
possessed the same faculty. As the teeth have so great a value in systematic zoology, 
it would be perhaps more advantageous to distinguish all Paridigitata into those 
which have tubercular and those which have crescentic teeth. To the first division will 
* The reduction of the limbs in Anoplotherium and Xiphoclon is so great that I regard them only as the last 
representatives of dying- out branches that did not leave any direct descendants. 
f If we except Hippopotamus — this last remnant of a Paridigitate series once rich in generic forms, hut 
which is now reduced to only two distinct groups. 
