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
Name day names in the Czech Republic gained slightly more importance than the others. For example, the dates associated with names Josef (Joseph) and Karel (Charles) are commonly known even by people with different names. However, the popularity of these names has decreased in the last years (6836 Josefs were born in 1947, but only 638 in 2014). Danes have their own calendar for name days (Danish 'navnedag'), see . However, the custom of celebrating one's name day is practically unknown in Denmark, and few Danes know when their name day is. Finnish Name Days Finns celebrate their name days (Finnish "nimipäivä",