seldom over half an inch long; it has the form of a polype, with long,

slender tentacles, but no special organs except a mouth and tubular stomach. Like the fabled hydra, if its head be cut off, another will grow out, and any fragment will, in the course of a short time, become a perfect hydra, supplying head or tail, or whatever is wanting, and hence the name given to the genus by Linnaeus."

Some of the hydroids are coral-makers. Fig. 2 represents the kind of work done by one of them. It certainly looks like a plant, and, in allusion to its delicate plumes, it is called Plumularia. Along