along the nasal cavity, the latter of which are used to detect chemical signals. Experiments on green sea turtles showed they could learn to respond to a selection of different odorant chemicals such as triethylamine and cinnamaldehyde, which were detected by olfaction in the nose. Such signals could be used in navigation. Breathing The rigid shell of turtles is not capable of expanding and making room for the lungs, as in other amniotes, so they have had to evolve special adaptations for respiration. The lungs of turtles are attached directly to the carapace above while below, connective tissue attaches them to the organs. They have multiple lateral (side) and medial (middle) chambers (the numbers of which vary between species) and one terminal (end) chamber. The lungs are ventilated using specific groups of abdominal muscles attached to the organs that pull and push on them. Specifically, it is the turtle's large liver that compresses the lungs. Underneath the lungs, in the coelomic cavity, the liver is connected to the right lung by the root, and the stomach is directly attached to the left lung, and to the liver by a mesentery. When the liver is pulled down, inhalation begins. Supporting the lungs is a wall or septum, which is thought to prevent them from collapsing. During exhalation, the contraction of the transversus abdominis muscle propels the organs into the lungs and expels air. Conversely, during inhalation, the relaxing and flattening of the oblique abdominis muscle pulls the transversus back down, allowing air back into the lungs. Although many turtles spend large amounts of their lives underwater, all turtles breathe air and must surface at regular intervals to refill their lungs. Depending on the species, immersion periods vary between a minute and an hour. Some species can respire through the cloaca, which contains large sacs that are lined with many finger-like projections that take up dissolved oxygen from the water. Circulation Turtles share the linked circulatory and pulmonary (lung) systems of vertebrates, where the three-chambered heart pumps deoxygenated blood through the lungs and then pumps the returned oxygenated blood through the body's tissues. The cardiopulmonary system has both structural and physiological adaptations that distinguish it from other vertebrates. Turtles have a large lung volume and can move blood through non-pulmonary blood vessels, including some within the heart, to avoid the lungs while they are not breathing. They can hold their breath for