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 Harrison performances" (just three of which date from the ex-Beatle's solo years) and described the track as an "exultant song of surrender", abetted by Harrison's "pumping fuzz guitar" and the song's "singalong magnetism". AllMusic's Richie Unterberger similarly praises "What Is Life" for its "anthemic" qualities, "particularly snazzy horn lines", and a guitar riff that is "one more entry in the catalog of George Harrison's book of arresting, low, descending guitar lines". Writing in the book "1,000 Recordings to Hear Before You Die", author Tom Moon refers to "the upbeat single 'What Is Life'" as an example of how Harrison "grabs