GENERAL INTRODUCTION 19 



like the anemones but consist of many individuals united 

 together. Of such are the little Hydroids which have 

 branching stems dotted with many little polyps, like flowers, 

 each one resembling a minute anemone, which are united 

 to one another by a common canal which traverses the stem. 

 The framework is usually of a thin, transparent, horny 

 material, though in a few cases it is of limy substance, the 

 result being a kind of coral. Some of these are not attached 

 at all, have no skeleton, and swim freely in the sea, an 

 example being the Portuguese Man-o'-War. Allied more 

 closely to the anemones are the false corals or Alcvonarians, 

 consisting of many individuals with a common skeleton 

 of thick horny substance or of tiny spicules or other material, 

 and also the true corals (Madreporaria) with massive limy 

 skeletons. 



The worms are divided into many groups with little 

 resemblance other than in shape. There are the little 

 flatworms or Turbellaria, seldom more than an inch long, 

 very flat and almost transparent, to which are allied many 

 parasitic worms which, though commonly found in marine 

 animals, need not concern us here. There are also the 

 Nemertina, soft-bodied worms with a long proboscis which 

 they can protrude or draw in at will, and without that 

 division of the body into a series of transverse segments 

 which is so striking a feature of the most highly-organized 

 worms. These are known as the Annelida and include 

 the common earthworm (in which the segments we have just 

 spoken of are very easily seen) and the bristle-worms 

 (Polychaetes) which are almost exclusively marine, being 

 everywhere abundant and constituting the great majority 

 of the marine worms. Besides segmentation they are 

 characterized by the presence of long bristles which project 

 from the sides of the body. Some wander about at will 

 and are called errant worms, but others live always in 



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