INTRODUCTORY AND EXPLANATORY xvii 
people who call for easier names do not stop to 
reflect that, in many cases, the scientific names are 
no harder than others, simply less familiar, and, 
when domesticated, they cease to be hard: witness 
mammoth, elephant, rhinoceros, giraffe, boa con- 
strictor, all of which are scientific names. And 
if, for example, we were to call the Hyracothe- 
rium a Hyrax beast it would not be a name, 
but a description, and not a bit more intelli- 
gible. 
Again, it is impossible to indicate the period 
at which these creatures lived without using the 
scientific term for it — Jurassic, Eocene, Plio- 
cene, as the case may be—because there is no 
other way of doing it. 
Some readers will doubtless feel disappointed 
because they are not told how many years ago 
these animals lived. The question ts often asked— 
How long ago did this or that animal hve? But 
when the least estimate puts the age of the earth 
at only 10,000,000 years, while the longest makes 
it 6,000,000,000, it does seem as if it were hardly 
worth while to name any figures. Even when 
we get well toward the present period we find 
the time that has elapsed since the beginning of 
