. Natural history. Zoology. HYDROID COLONIES. 697 shapes, break off and swim away as minute Jelly-fish (Fig. 6, B), dispersing their young as they go. Before giving any further account of these reproductive individuals, we must describe the Hydroid colonies a little more closely. They frequently resemble delicately branching trees or bushes, fine moss, or feathers, or sometimes form crusts over stones—hence the name of Zoophytes or animal- plants. Such growths are very common on our coasts, and are still popu- larly considered, on account of their plant-like appearance, to be sea-weeda ; this
. Natural history. Zoology. HYDROID COLONIES. 697 shapes, break off and swim away as minute Jelly-fish (Fig. 6, B), dispersing their young as they go. Before giving any further account of these reproductive individuals, we must describe the Hydroid colonies a little more closely. They frequently resemble delicately branching trees or bushes, fine moss, or feathers, or sometimes form crusts over stones—hence the name of Zoophytes or animal- plants. Such growths are very common on our coasts, and are still popu- larly considered, on account of their plant-like appearance, to be sea-weeda ; this deceptive appearance being heightened by the fact that the very minute polyps forming the colony are, in many cases, when contracted, entirely hidden within the protective framework. This common protective covering is sometimes of a horny nature and transparent, sometimes hard and chalky, and, round the bodies of the individuals of the colony, may take the form of cups into which the soft polyps can withdraw. The Campanularians received their name from their bell-shaped, protective cups. In the Sea-firs or Sertu- laria, the cups project from each side of the stalk; in the Plumularians, from only one side. In other forms, again, there are no protective cups. The Oaten straw coralline (Tubularia) resembles a number of closely-packed straws, from the ends of which the beautiful little crimson-tentacled polyps project. Besides these colonies which invest themselves with hard, tubular cover- ings, there are others in which the chalky parts become so greatly developed as to form massive skeletons so like those of Corals that they were long classed as such. These Hydrocorallia are The often found in coral reefs, and would be taken, by the Hydrocorallia. uninitiated, for true coral. In one family, the skeleton of which exactly resembles that of a branched, pink coral, the similarity is even carried out in the structure of the polyp. This family has received the name of the Stylasteri
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