234 



COCKROACHES. PHYLUM ARTHROPODA 



RESPIRATORY ORGANS 



The respiratory system consists of branching tubes or trachese 

 (Fie 1 69) of ectodermal origin with a spirally thickened 

 lining of 'cuticle, which arise from ten pairs of opemngs or 

 stigmata at the sides of the body. There are two large stigmata 

 on each side of the thorax, one between prothorax and meso- 

 thorax, one between mesothorax and metathorax, and m each 

 of the first eight abdominal somites a stigma is placed on each 











r-fex,"^"- 



^.p/)W. 



cu. 



Fig. 170.— A portion of the tracheal tissue of a cockroach, highly magnified. 



Only parts of the tubes are in focus. 



cu Cuticular lining with spiral thickening ; nu., nuclei of the protoplasmic layer; ppm., protoplasmic 

 ' layer continuous with the epidermis (hypodermis) of the surface of the body. 



side between the tergum and the sternum. Air is pumped in and 

 out of the larger tracheae by contraction and expansion of the 

 abdomen, and by diffusion renews the gases in the fine branches 

 of the tracheal system (tracheoles) , which have no cuticular 

 lining, ramify in the tissues, and end upon or actually in the cells. 

 (Figs. 170, 171). 



When the insect is at rest the ends of the tracheoles are full 

 of fluid. When the muscles are active, products of their metabolism 

 raise the osmotic pressure in the tissues, and this withdraws the 

 fluid so that air extends more deeply into the tracheoles and 



