The Life Processes of the Individual 151 



RESPIRATION 



That an animal may live, it must have oxygen. The 

 oxygen taken into the body in respiration does not go to 

 form protoplasm in the various cells but it is used to com- 

 bine with the products of katabolism to make simpler com- 

 pounds which can be eliminated from the body. These 

 products of the breaking down of the living substance are 

 of such a character that they poison the cells unless they 

 are promptly removed. The process is like ordinary com- 

 bustion in that these products combine with oxygen to 

 form carbon dioxid and water and to generate heat. 



In man, the oxygen is taken into the lungs and the blood 

 is pumped there to meet the oxygen. But the bee does not 

 have a closed circulation which will effectually carry the 

 blood to the oxygen. Furthermore, the higher animals 

 have in their red blood corpuscles a substance, haemoglobin, 

 which is capable of absorbing abundant oxygen, but this is 

 lacking in the colorless blood of insects. In the bee, instead 

 of the blood being carried to the oxygen, the oxygen is 

 carried to the blood by means of tracheal sacs and a multi- 

 tude of tracheal branches which go to every organ and to 

 every part of the bee's body. These tracheae receive their 

 air supply through openings in the outer wall, the spiracles, 

 two pairs on the sides of the thorax and eight pairs on the 

 abdomen. The tracheae are composed of a delicate epi- 

 thelium lined with a thin layer of chitin. To prevent the 

 collapse of the tracheal trunks, some of them are further 

 strengthened with spirally placed rings of chitin, which 

 are thickenings of the chitin lining. The finer branches 

 lack these chitin rings and there are few heavy trunks in 

 the bee, the walls usually being delicate. 



The oxygen is therefore carried to all parts of the bee's 

 body, passes through the walls of the tracheal system, is 

 absorbed by the blood and is carried to every cell. The 

 products of katabolism are in turn carried by the blood, 

 and the water vapor (at least most of it) and the carbon 



