the slightest movement of your hand towards him, he is gone! He has retreated like a lightning-flash into his tube. But did you notice how cleverly, as he went, he shut the door after him? A most marvellous contrivance is here. Watch it as it again carefully protrudes. There is a solid organ exactly conical, seated at the end of a long flexible stem, which forms the stopper; it is one of a pair of tentacles, but as only one could be of any service as a stopper, one only is developed; the other being minute. This stopper is very beautiful; it is always richly coloured, usually orange, or vermilion, sometimes varied with pure white: its flat extremity or top is made up of ridges, which run from the centre to the circumference, where they project in tiny teeth of the most exact regularity. The fan-like expansions are formed of radiating filaments, also very brilliant in hue, which are the breathing organs, separating oxygen from the currents of water which play along their ciliated surfaces.
There is no distinct head in these animals, but the organs I have described are protected by a sort of projecting mantle or hood, beneath which is the orifice of the stomach. Eyes it seems to have, and most sharp ones; for, as we saw, the animal is peculiarly sensitive to the approach of any object, even though this be on the outside of a glass tank, at the bottom of whose interior it is expanded. Yet I have searched in vain for any distinct organs of vision.
The mechanism by which the Serpula projects its body from its shelly tube, and by which it withdraws on alarm with such inconceivable rapidity, is won-
