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 .'' 



Thj 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 tlie 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 trachecz. A tradiea 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 tracheae through several openings like 



