50 
THE STUD Y OF INSECTS . 
the term to the Hexapoda, and it is in this sense that we 
use it. 
The name Hexapoda is from two Greek words: hex, six ; 
and pons, foot. It refers to the fact that the members of 
this order differ from other Arthropods in the possession of 
only six feet. 
Insects breath by means of a system of air-tubes (tra¬ 
cheae) which extends through the body. This is true even 
in the case of those that live in water and are supplied with 
gill-like organs (the tracheal gills; see p. 75). The head is 
distinct from the thorax, and bears a single pair of antennae; 
in these respects they are closely allied to the Myriapods. 
But they can be easily distinguished by the number of their 
feet, and, usually, also by the presence of wings. 
The Metamorphoses of Insects. 
Nearly all insects in the course of their lives undergo re¬ 
markable changes in form. Thus the butterfly, which de¬ 
lights us with its airy flight, was at one time a caterpillar; 
the bee, which goes so busily from flower to flower, lived first 
the life of a clumsy, footless grub; and the graceful fly was 
developed from a maggot. 
In the following pages considerable attention will be 
given to descriptions of the changes through which various 
insects pass. It is our wish in this place merely to define 
certain terms which are used in describing these changes. 
Development without Metamorphosis. —In one of the orders 
of insects, the Thysanura, the young insect just hatched 
from the egg is of the same form as the adult insect. These 
insects merely grow larger, without any more marked change 
in form than takes place in our own bodies during our life. 
They are said, therefore, to develop without metamorphosis. 
Incomplete Metamorphosis. —There are many insects which 
undergo a striking change of form during their life* although 
the young greatly resembles the adult. Thus a young locust 
just out from the egg can be easily recognized as a locust. 
