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
What Is Life "Rolling Stone" readers' poll, titled "10 Greatest Solo Beatle Songs", the song placed fourth, with the editor commenting: "The track is deceptively simple, and more layers become apparent the more often you play it." "What Is Life" has featured in Bruce Pollock's book "The 7,500 Most Important Songs of 1944–2000", Treble website's "The Top 200 Songs of the 1970s" (ranked at number 101) and Dave Thompson's "1000 Songs That Rock Your World" (at number 247). "What Is Life" was included on the 1976 compilation "The Best of George Harrison" as well as 2009's "". The song has also been featured