AMPHIBÆNA AQUATICA, a name given by Bertrius, Albertus, and several other authors, to that long and slender insect, called by others the feta aquatica, and vermis fetarius. It has the name amphibæna, from its going backwards or forwards with equal ease and celerity. The usual size is four or five inches long, and the thickness of a large hair.
Dr Lister accidentally found out the origin of this worm, in his researches into the history of a very different sort of insect. Dissecting one of the common black beetles dug up in a garden, he found in its belly two of these hair worms, or amphibæna; and renewing the experiment on other beetles of the same species, he found that they usually contained, one, two, or three of these worms. As soon as the body of the beetle is opened, they always crawl out. When put into water they will live a considerable time, and swim nimbly about; but often put up their heads above water, as if endeavouring to make their escape, and sometimes fastening themselves by the mouth to the sides of the vessel, and drawing their whole bodies after them. These creatures are not only found in the waters, but buried in earth, and sometimes on the leaves of trees, in our gardens and hedges. Phil. Trans. No 83.