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
Less Commonly Taught Languages Less Commonly Taught Languages Less Commonly Taught Languages (or LCTLs) is a designation used in the United States for languages "other than" the most commonly taught foreign languages in US public schools. The term covers a wide array of world languages (other than English), ranging from some of the world's largest and most influential languages, such as Chinese, Russian, Arabic, Hindi, Portuguese, Japanese, Persian, and Turkish, to smaller regional languages studied in the US mainly by area experts, such as Twi, spoken in West Africa, and Finnish. The term arose out of a need to contrast the more commonly taught