58 



The Form of Insects 



pass to the head, legs and wings, breaking up into 

 minute branches and ramifying to the farthest parts 

 of the appendages (hg. 41). 



Microscopic study of an air-tube shows that its 



Fig. 40. — Ventral portion of air-tubes in 

 Cockroach. Magnified 2^ times. 

 After Miall & Denny. 



Fig. 41. — Air-tubes in head and jaws of Cock- 

 roach. A. D. main paired trunks ; C. branch 

 to brain ; E. to feelers ; F. to jaws ; G. to 2nd 

 ma.xillEE ; H . J . to ist ma.xilia; ; /. to man- 

 dibles and labrum. Magnified 73 times. 

 From Miall & Denny. 



wall is composed of three layers, a thin outer base- 

 ment membrane, a central layer (epithelium) of large 

 polygonal cells and an inner layer of chitin, con- 



