Trachea Diffusion of oxygen and carbon dioxide takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph. This is one of the factors that may limit their size. A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries such as loops or helices. Taenidia provide strength and flexibility to the trachea. In the head, thorax, or abdomen, tracheae may also be connected
History of beliefs about the human body these views, that the soul has aspects that can't be felt by normal methods, and physical manifestations that can be felt. "For even if one and being are spoken of in several ways, what is properly so spoken of is the actuality" -Aristotle in DeAnima Aristotle forms the idea of Hylomorphism, that the soul and the body are not capable of being split apart without destroying both in the process. Despite this idea of the body and the soul Aristotle viewed disorder in what could be seen and felt. He was a proponent of the humoral theory that classified disorder