240 THE HAUNTS OF LIFE 
It has its drawbacks, this instinctive capacity, 
but it makes for success as long as the unex- 
pected does not happen. 
The fourth reason for the surpassing success 
of insects in the system of animate nature is 
to be found in their variability or plasticity, 
linked with that of the plant world. While 
the fundamentals of an insect’s body are al- 
ways the same, the details vary without end, 
and this has enabled insects to find an unusual 
number of niches of opportunity, especially 
in their vital linkages with the likewise very 
variable, flowering plants. Now, the more 
niches of opportunity a class of animals can 
find, the greater will be its success. 
A Russian naturalist, Chetverikov, has 
called attention to a fifth reason for the suc- 
cess of insects. It concerns their skeleton. In 
backboned animals the skeleton—of living 
gristle or bone—is inside the body; in insects 
and other jointed-footed (Arthropod) animals 
the skeleton—of not-living chitin—is outside 
the body. Now it is argued that this entirely 
different kind of body architecture made it 
possible for insects to become very minute 
without ceasing to be very effective. It was 
more practicable to become small when the 
