RESPIRATION OF INSECTS. 



25 



Fig. 14. 



STIGMATA. 



ESPIRATORY ORGANS. 



60. All insects have an aerial 

 respiration ; but instead of re- 

 ceiving air into pulmonary 

 cavities to which the blood is 

 sent by the action of the circu- 

 lating organs, as is the case in 

 most animals, they breathe by 

 means of a multitude of canals 

 (Jig. 13) which convey the air 

 to every part of the body ; these 

 canals are named trachea. The 

 external openings of the tra- 

 cheae are called stigmata or 

 spiracles. These openings have 



the form of a 



button-hole (Jig. 



14), and are 



placed on each 



side of the body. 



In this respect, 



the organization 



oftracheal arachnidans resembles that of insects. 

 51. Sometimes the trachea have enlargements along their 

 course like vesicles ; they all communicate freely 

 with each other ; they are ramified like roots, 

 and their last divisions penetrate into the sub- 

 stance of the organs. Their structure is the 

 same as in tracheal ara'chnidans, that is, they 

 are formed of a cartilaginous filament rolled 

 spirally, so as to constitute a tube (Jig. 15). 

 Were it not for this arrangement the sides of the tube would 

 be forced together by atmospheric pressure, and the animal 

 would be suffocated for want of air. Respiration seems to be 

 effected by the movements of the abdomen. In insects this func- 

 tion is very active: considering their size, they consume a con- 

 siderable quantity of air, and quickly suffocate when deprived of 



Explanation of Fig. 13. Respiratory apparatus of insects. The mask 

 or covering of on insect, showing the principal tracheae which convey air to 

 all parts of the body ; s, s, s, s, s, the stigmata or spiracles. 



Explanation of Fig. 14. A stigmata magnified; s, the opening of the 

 stigmata or spimcle; ir, a tracheae arising from it. 



Explanation of Fig. 15. A portion of tracheae considerably enlarged to 

 show its structure ; we see at (a) the end of the spiral of which the tube ia 

 composed, partly unrolled. 



50. How do insects breathe ? What are tracheae ? What are stigmata * 



51. How are the tracheae arranged? What is the peculiarity of their 

 str LU ture ? 



3* 



Fig. 15. 



TRACHEA. 



