8 A FIRST CHAPTER 
that without the aid of the intermediate forms the relationship between 
the twv would not be suspected. The direct relatives of many reptiles 
are found much further back than are those of mammals, while some 
living fishes belong to the same family and even the same genus as those 
that existed so long ago as the Cretaceous Period. As for invertebrates, 
and especially some shellfish, a few go back unchanged for periods of 
time representing millions of years; down in the depths of the sea, in 
uniform quiet, cold and darkness, they have lived an unvarying exist- 
ence for zons of time, while what we term the eternal hills have been 
washed away, and others upheaved to take their places. 
Thus evolution, or change among animals, has gone on more and 
more rapidly as higher forms came into existence. 
Knowing the great changes that have taken place among animals 
since they first appeared in the world, we are able to account for existing 
differences we find between them. Some groups have steadily progressed, 
a few have degenerated; some have diminished in numbers and many 
have disappeared. 
If we open a fan, and imagine that the sticks represeat various divi- 
sions of animals, we shall have a rough illustration of what might have 
taken place had their development been uniform; all have a common 
point of origin, but the farther we go from this poiat, the more widely 
are they separated, although the relationship of one to another may 
easily be seen. If now we break some of the sticks at differeat places 
and whittle down some of the ends, we shall have gaps of varyiag widths — 
at various places, and the ends will be of unequal size and at irregular 
distances from one another, as are the groups of living animals. 
For example, while there are but two living species of elephants, one 
ia Asia, and another in Africa, fossil remains indicate that there were 
formerly a large number of species inhabiting all the continents save 
Australia. And, as the history of the elephants is followed backwards, we 
find, even with the small amount of material now at our disposal, that 
their characters gradually change, and that they may be traced to much 
smaller animals not unlike tapirs. In this instance, not only are the 
sticks of the fan broken, but the one representing the elephants is 
whittled down to two species. The horse is probably the best example 
we have of an unbroken line of descent, and most educated people are 
aware that its pedigree may be traced to a race of animals no larger than 
a collie dog which also gave rise to other and very different groups of 
animals. The stick representing the horse family is entire, but not so 
large as it was. 

