Images Dated 4th March 2004

Sea fan and seahorses, X-ray

Sea fan coral. Coloured composite X-ray of two seahorses above a sea fan, or gorgonian. Sea fans are coral-like organisms that live in a large colony. Each organism, or polyp, secretes a hard mineral around itself for protection and support. These secretions form the rocky skeleton seen here. Sea fan polyps feed by sifting minute plankton particles from the water. Sea fans are flat, and are orientated to present the maximum surface area to the prevailing current. Seahorses are fish that inhabit reefs and reeds throughout the world's temperate and tropical seas. They grasp onto structures such as coral with their prehensile tails

© D. ROBERTS/SCIENCE PHOTO LIBRARY

Atherosclerosis

Atherosclerosis. Artwork of a human heart showing narrowing of the coronary arteries due to atherosclerosis, a build up of fatty deposits (atheroma, yellow) on the artery wall. The large red vessel is the aorta, the main artery carrying blood from the heart to the body. Two coronary arteries arise from the aorta and supply the heart muscle with oxygen. The left coronary artery (on the right) divides into the anterior descending and circumflex branches. Coronary artery disease is the most common cause of death in developed countries. The narrowing causes abnormal clotting, which blocks the vessel and starves the heart's muscle of blood, causing a heart attack

© JOHN BAVOSI/SCIENCE PHOTO LIBRARY

Volcano caldera formation

Caldera formation. Artwork of the formation of a caldera, a large basin-shaped volcanic depression. Calderas may form when a volcano (top) undergoes a massive eruption (upper centre). This creates a much larger crater than the original volcanic vent (lower centre). Alternatively, the volcano may collapse inwards. Over time the magma chamber beneath the caldera solidifies and the volcano becomes dormant or extinct. The caldera may then fill with water to form a lake (bottom). Renewed volcanic activity may lead to the formation of new volcanic cones within the caldera. A well- known caldera lake is Crater Lake in Oregon, USA, which is more than 600 metres deep

© GARY HINCKS/SCIENCE PHOTO LIBRARY