The sperm whale is the largest of the toothed whales, with males growing up to 20 metres in length. It also has the largest brain of any living animal, and it was a sperm whale that was pitted against Captain Ahab in Herman Melville's classic novel, Moby Dick (2). Sperm whales have huge square heads, comprising almost a third of the total body length (2) (3); indeed the specific name macrocephalus means large head. Uniquely among cetaceans, the single blowhole is located on the left of the head rather than on the top (3) and so these whales are easily identified at a distance by their low, bushy spout, which is projected forward and slightly to the left (2). Further down the body toward the tail there is usually a large hump on the back, followed by a series of smaller bumps (3). The dark brown to bluish-black skin, which is splotched and scratched, is said to have a texture like that of a plum stone (2) (3). Males tend to be somewhat larger and heavier than females (3), and have larger heads in relation to their body size (6). The huge heads of sperm whales contain a large cavity, the spermaceti organ, filled with a waxy liquid called spermaceti oil. This wax can be cooled or heated, possibly by water sucked in through the blowhole, and thus shrinks and increases in density (helping the whale sink), or expands and decreases in density (helping the whale rise to the surface) (5). Whalers likened the substance to semen, and this is the origin of the common name of the species (6).
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