One large group has the peculiarity of multiplying by division, the last joints or segments being devoted to the formation of the new individual. At one time of the year the ordinary sexual process of reproduction takes the place of this method, and each worm is then surrounded by a belt such as may be seen in the common earthworm under similar conditions. Further information on this subject is greatly needed. The type is the common _Naïs_, which has a body of thirty segments or more, two eye-specks on the head, and a double row of bristles along the back; whilst below, each segment carries strong hooked bristles, nearly buried in the body, by means of which the worm crawls. Inside the mouth is a large proboscis, which can be protruded, and this leads into a stomach which is merely an enlargement of the intestine which succeeds it. The circulation of the blood (which is colourless) can be easily watched. It begins at the tail with a contraction of the dorsal vessel, passes up to the head, and then down below the intestine to the tail again. The intestine is ciliated inside, and it is by a current of water carried into the intestine by these cilia that the blood is aërated. In the next genus, _Dero_, this is clearly seen, for the tail (Plate XIV. Fig. 1) is opened out into a wide shield, from which rise four, six, or even eight finger-like processes. These parts are all ciliated, and contain a network of blood-vessels. The worm lives in a case which it builds in the mud, and the way to find it is to put some of the mud into a glass beaker with water, and allow it to stand. If there be members of this family in it, their tails will be seen protruding above the water. Pour out the mud sharply, fill up with water, and allow the dirt to subside, and the worms may then be made to leave their cases by pressure by a camel hair pencil on the lower end of the tube, and may be caught with the dipping tube and placed in the live-box. They have no eyes, otherwise the general outline of the body closely resembles that of Naïs. _Slavína_ (Fig. 2) has a row of touch-organs, like pimples, round each segment, and is a dirty looking creature, with an inordinately long first pair of bristles, but this reaches its acme in _Pristina_ (Fig. 3) (sometimes, though wrongly, called _Stylaria_) _parasita_, which has three long sets of bristles upon the back, and keeps these in constant wing-like motion. The true _Stylaria_ has a long trunk, set right in the head, and tubular (Fig. 6); it grows to a considerable length, and when in the stage of fission it is very funny to see the two proboscides waving about, one on the middle, as well as the original one at the head. There is also a form with a shorter proboscis of the same kind.