Spermaceti

Spermaceti (from Latin sperma meaning "semen", and ceti meaning "whale") is a waxy substance found in the head cavities of the sperm whale (and, in smaller quantites, in the oils of other whales). Spermaceti is created in the spermaceti organ inside the whale's head.

Two theories for the spermaceti organ's biological function suggest it either controls buoyancy, or acts as a focusing apparatus for the whale's sense of echolocation. There has been concrete evidence to confirm both theories. The buoyancy theory holds that the sperm whale is capable of heating the spermaceti, lowering its density and thus allowing the whale to float; in order for the whale to sink down again, it must take water into its blowhole which cools the spermaceti into a denser solid. This claim, however, has been called into question by recent research which indicates a lack of biological structures to support this heat exchange, as well as the fact that the change in density is too small to be meaningful until the organ grows to huge size.