THE METAMORPHOSES OF THE NERVOUS SYSTEM. 45 
“At fifty-eight hours the middle part of the chest has greatly 
increased in size, and the great nervous centres and nerve twigs 
which will supply the wings eventually with energy occupy it. 
The optic and antennal nerves have nearly attained their full 
development, and the arrangement of the whole nervous system 
is now nearly as it exists in the perfect insect. The whole of 
these important changes are thus seen to take place within the 
first three days after the insect has undergone its metamorphosis, 
and they precede those of the digestive system.” The nervous 
system is matured first of all. Newport considers that the con- 
traction of the muscles which draw up the segments of the body 
as metamorphosis proceeds, initiates and influences these wonderful 
changes in the nervous structures. 
If the alterations in the nervous structures are wonderful, what 
must be said of the changes in the activity, in the instincts, in 
the amount of energy and will, and in the whole of the habits 
that spring into existence when the perfect insect emerges into its 
peculiar life ? 
The study of the metamorphosis of the structures which enable 
insects to breathe and thus keep up their heat and the purity of 
their blood, and to become more or less filled with air during their 
flight is almost as interesting as that of the nervous system. 
When an insect is placed in water and opened carefully, beautiful 
tiny tree-like branches of silvery-looking threads are noticed cover- 
ing the digestive organs, entering amongst the tissues and on the 
inside of the skin. If the microscope be used these threads can 
be seen to divide, subdivide, and unite, and their minuteness is 
wonderful. They are called ¢rachee. A trachea is a tube formed 
by two layers of membrane, between which is a spiral thread. 
It is kept open by the spiral, which is capable of much com- 
pression, so that the quantity of air any trachea may contain 
varies according to circumstances. They are the very perfection 
of delicacy of structure combined with elasticity. The centre 
of each trachea is occupied by air, and the layer of membrane 
in contact with it is continuous with the outside skin of the body. 
The spiral tissue is produced during the growth of the insect, and 
the fine membrane which covers it acts like a loose investment. 
The outside air enters the trachee through several openings like 
