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) to mortality and human connections, is childlike in her innocence and questions. Xander's anger and Anya's confusion allow them to be mothered somewhat by Willow, who needs to take care of someone. Dawn is deeply in denial, unable to understand that the woman she thought she had known all her life was gone. Tara, who has gone through the ordeal before, represents the acceptance phase, soothing and helping the others to work through what they are experiencing. Buffy toward the end also begins to see acceptance when she tells Dawn that the body in the morgue is not their mother;