Pond Life 
oak-tree, fixed in the same place for 
hundreds of years, and a freely moving 
mammal or flying bird. But the 
mammal, and the bird, and the oak, can 
all be traced backwards by means of 
their earlier forms, through such a space 
of time that we have no means of count- 
ing it, until we arrive at a thing, a living 
creature, which can hardly be said to 
be either plant or animal. It seems to 
have some of the characters of each. 
It may even resemble at one period 
of its life a plant, and at another an 
animal. From some such lowly creature 
must have sprung other forms, some 
of them more animal, and others more 
vegetable, until finally they branched 
out into quite different directions, one 
branch ending in plant life, the other 
in animal life. 
I22 
