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
The Body (Buffy the Vampire Slayer) and Dawn. She asks why her clothes are stupid and she is childish, weeping until Tara kisses and calms her. Anya asks Xander what she is supposed to do; he cannot answer. Willow changes her shirt again and Xander expresses his desire to find Glory and exact justice, then complains about Joyce's negligent doctors. Anya asks if they will see the body, then if the body will be cut open, and Willow responds angrily. Anya tearfully says she does not understand how to behave, or why Joyce cannot go back into her own body, unable to understand human death, she