330 MOSTLY MAMMALS 
between Southern Europe or Ireland, or between Ireland 
and North America, seems altogether out of the question 
within any period during which the fauna can have been 
specifically identical with that of the present day. The 
only conclusion is that from ancestors, presumably of the 
same genus, which took to an underground life in such 
widely separated localities, the similar conditions of the 
caves have evolved descendants so similar that when com- 
pared they cannot, or can hardly, be specifically distinguished 
from each other.” 
Should these identifications be confirmed, it will be evident 
that the same, or closely allied species, have originated inde- 
pendently in different caves, and although the author cited 
is of opinion that this phenomenon may only hold good with 
regard to cave-animals, it is possible that it may be found 
also to exist in the outer world, since it has been suggested 
that the horses (Zguus) have originated independently in 
the Old and New Worlds from different ancestral stocks. 
