THE INTERNAL ANATOMY OF INSECTS 111 



ments by one or more longitudinal tracheae, and is also connected 



Fig. 133. The tracheae of Machilis (From Oudemans). 



with the group on the opposite side of the same segment by one or 

 more transverse tracheae (Fig. 134). 



The structure of the tracheae. The fact that 

 in their embryological development the tracheae 

 arise as invaginations of the body-wall, makes it 

 easy to understand the structure of the tracheae. 

 The three layers of the body-wall are directly- 

 continuous with corresponding layers in the wall 

 of a trachea (Fig. 135). These layers of -a 

 trachea are designated as the intima, the epithe^ 

 Hum, and the basement membrane. 



The intima is the chitinous inner layer of the 

 tracheae. It is directly continuous with the 

 cuticula of the body- 

 wall, and like the 

 cuticula is molted at 

 each ecdysis. 



A peculiar feature 

 of the intima of 

 tracheae is the fact 

 that it is furnished 

 with thickenings 

 which extend spirally^ 

 These give the 



Fig. 134. Larva of tracheae their charac- Fig. 135. Section of a trachea 



Cantharis vesicatoria, t .,. f q i and the body-wall; c, cuti- 



showing the distribu- l cula; h, hypodermis; bm, 



t.irm of trflr.he.ap! CFrom striated appearance, basement membrane; sp % 

 Henneguy after jf f f spiral thickening of the ih- 



Beauregard). tima, the taenidium. . 

 the larger tracheae be 



pulled apart the intima will tear between the folds of the spiral 

 thickening, and the latter will uncoil from within the trachea like a 



