On the other hand, the power to move in search
of their food, which is not equally diffused, becomes a most
important advantage to the feeders on other organisms. They
therefore develop various means of locomotion. Some flow or roll
slowly along like tiny drops of oil on an inclined surface;
others develop minute outgrowths of their substance, like fine
hairs, which beat the water as oars do. Some of them have one
strong oar, like the gondolier (but in front of the boat); others
have two or more oars; while some have their little flanks
bristling with fine lashes, like the flanks of a Roman galley.
If we imagine this simple principle at work for ages among the
primitive microbes, we understand the first great division of the
living world, into plants and animals. There must have been a
long series of earlier stages below the plant and animal. In
fact, some writers insist that the first organisms were animal in
nature, feeding on the more elementary stages of living matter.
At last one type develops chlorophyll (the green matter in
leaves), and is able to build up plasm out of inorganic matter;
another type develops mobility, and becomes a parasite on the
plant world.
Pages:
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135