History of All Animals 53

ON PENICILLI

Certain shelly tubes are called *Penicilli* (or "pencil-shells") by modern authors because they contain a substance within their cavity that resembles the brushes or pencils used by painters. According to the opinion of Rondelet, these are attached to rocks by a soft and loose substance, so that they may easily yield to and be moved by the surging waves. When the fleshy part that lies hidden within emerges, it expands into a leafy form, as depicted in Rondelet’s illustrations—though there are many other tubes in which worms are known to lurk. Finally, there are others said to live within sponges, which are shown in the following images, even though some authors maintain that these spiral shells are actually a species of *Dentalium*.

Living within sponges in the manner of Penicilli

SUPPLEMENT TO THE