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
Facebook real-name policy controversy the acronym is employed, Facebook automatically changes to lower-case all letters except the first. (Use of periods, e.g. D.L.G., will result in a message telling users that "Profile names can't have too many periods.") Therefore, someone commonly known in real life by a name such as Mary De Leon Guerrero Mafnas would have to resort to using what on Facebook would end up being "Mary Dlg Mafnas". The message is not accompanied by an option to challenge/appeal the restriction or to send Facebook documentation that the format is how one normally formats their name in real life. In January 2015,