The bestiary is a type of medieval book organized in the manner of a dictionary and containing entries on animal (or vegetable) physiology. Bestiaries often described fanciful or mythical creatures, such as the Barnacle Goose--a bird popularly supposed to hatch from shells growing on trees. They were lavishly illustrated and often contained representations of a symbolic or alchemical nature. The bestiary descended from the Physiologus, a book known to be in existence in the fifth century organizing the elements of natural science. The bestiary exemplifies ideas found in the concept of the book of nature, for example, the conception of the world as either the product of text (the divine word) or reducible to text (the quantitative and qualitative scriptures of science). Bestiaries displayed in the British Library date from 1230.