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Insect Tracheoles Introduction: Insect Tracheole gas exchange systems are commonly studied as part of many animal diversity courses because they are so dissimilar to any other animal system. Gases are transported from spiracles (openings along the abdomen) by a series of branching hollow tubes (trachea) to the tissues where oxygen is required and where carbon dioxide is produced. The fine tubules that deliver oxygen to the tissues themselves are called tracheoles and often have a film of moisture in their extremities. This system has its limitations because it is essentially a one-way system and relies heavily on diffusion for gas movement (particularly if the insect is at rest). Many insects employ pumping mechanisms when they are active and these mostly involve the action of muscles in the abdomen. Method Cockroaches are suitable for this exercise as they are large enough to handle easily. A freshly killed cockroach is dissected by cutting along its sides from the posterior end. Use a pointed pair of scissors as shown by the two arrows on the photograph at left. When the two cuts have been made lift off the ventral (front) surface (much like opening the cover of a book) to expose the body contents. The tissue you look for is muscle tissue. It is recognised because it has a light pink ‘meaty’ appearance. There is a large amount of muscle material in the region of the legs and wings in the thorax. Muscle tissue Start here Remember insects have 3 body parts; head, thorax and abdomen. In the thorax are the muscles that are responsible for walking and flight. Remove small portions of this muscle tissue. Place on a slide in 0.9% salt solution (or water). You might need to squash the preparation slightly or else tease out the muscle fibres with two needles before you add the cover slip. Images Air bubble inside trachea The four photographs on this page were taken at Low Power (x40) top right, or Medium Power (x100) for the other photographs. They show larger trachea that branch into smaller and smaller tubes that deliver oxygen to all tissues. Note the circular rings of chitin that supports the trachea and keeps them open. The exoskeleton is made of this same material. Air inside trachea These four photographs show the smaller tracheoles. The top pictures were taken at Medium Power (x100) and the bottom two were High Power (x400). Note how the trachea branch finely so that no muscle cells are far from their supply of oxygen.