VI EVOLUTION IN BIOLOGY 225 
Both Mr, Darwin and Mr. Wallace lay great 
stress on the close relation which obtains between 
the existing fauna of any region and that of the 
immediately antecedent geological epoch in the 
same region; and rightly, for it is in truth in- 
‘conceivable that there should be no genetic 
connection between the two. It is possible to put 
into words the proposition that all the animals and 
plants of each geological epoch were annihilated 
and that a new set of very similar forms was 
created for the next epoch ; but it may be doubted 
if any one who ever tried to form a distinct mental 
image of this process of spontaneous generation on 
the grandest scale, ever really succeeded in real- 
ising it. 
Within the last twenty years, the attention of 
the best palzeontologists has been withdrawn from 
the hodman’s work of making “new species” of 
fossils, to the scientific task of completing our 
knowledge of individual species, and tracing out 
the succession of the forms presented-by any 
given type in time. 
Those who desire to inform themselves of the 
nature and extent of the evidence bearing on these 
questions may consult the works of Riitimeyer, 
Gaudry, Kowalewsky, Marsh, and the writer of the 
present article. It must suffice, in this place, to 
say that the successive forms of the Equine type 
have been fully worked out ; while those of nearly 
all the other existing types of Ungulate mammals 
VOL. I @ 
