_Bohemilla_ has a tremendous array of saw-like bristles upon the back, whilst _Chætogaster_ has none at all in this position, and few below. _Æolosoma_ has merely tufts of hair instead of bristles, and swims freely. It is easily recognised by the red, yellow, or green pigment spots in its skin, and by the ciliated head. Rarest of all the family is the one which connects it with the ordinary _Tubifex_, the red worm which lives in masses in the mud of brooks and ponds, the waving tails protruding above the water, and being instantly withdrawn when a foot is stamped upon the bank. Their Naid cousin is _Naidium_, and has red blood, but multiplies by fission, which Tubifex does not. Another group of worms is the _Planarians_, small leech-like worms, black, white, or brown, which are rarely absent from a gathering. The would-be investigator will find in them an abundant field for work, as they are but very imperfectly known or studied. The great enemy of all these worms is the _Hydra_, a good idea of which may be formed from Plate IX. Fig. 13. There are three species, all of which are fairly common. They capture their prey in exactly the same way as sea-anemones and the marine hydroid forms, so numerous and varied. Nor must we omit to notice the exquisitely beautiful Polyzoa, such as _Lophopus_ (Plate XIV. Fig. 4), with its ciliated tentacles and transparent social home; _Fredericella_ (Fig. 5), with its graceful stems, and their still more graceful inhabitants; and the wonderful _Cristatella_, whose colonies form bodies which crawl over the stems of water plants. But for grace, beauty, and variety, the Rotifers assuredly outshine all their fellow inhabitants of our ponds and streams.