Tracheal System

 The tracheal system is found in land arthropods, a very successful terrestrial animal phylum. In these animals, air enters the body through small openings called spiracles located along the sides of the body. the spiracles lead into tubes called tracheae, which branch repeatedly within the body tissue. The smaller branches as called tracheoles. The smallest tracheoles contain fluid in which oxygen dissolves before actually reaching the individual body cells. In many flying insects, some of the tracheae expand to form thin walled air sacs. The spiracles, tracheae and tracheoles make up the tracheal system.

    The tracheal system is not linked to the circulatory system. This means that oxygen has to diffuse from the final tracheole to the individual cells. Since diffusion can only occur effectively over very short distances, animals that breathe by tracheae are small (usually with a body that is not more than tow centimeters wide). Generally, arthropods, especially flying insects, are very active as the efficient tracheal system provides them with a plentiful supply of oxygen. (A large amount of energy is needed for flight.).