MAEINE WOEMS 177 



is often of great length. Their bodies are not distinctly segmented, 

 nor do they bear any appendages. The skin is tough and horny, 

 and the body-wall, which is very thick and muscular, is often 

 contracted when the animal is disturbed, thus causing a jet of water 

 to be forcibly ejected. 



All the most interesting of the marine worms belong to the 

 Annelida or Chcetopoda, popularly known as the Bristle-footed 

 worms, because their locomotion is aided more or less by the 

 presence of stiff bristles that project beyond the surface of the 

 skin. These are all highly organised worms, mostly with very 

 elongated bodies that are distinctly segmented exteriorly by a 

 number of transverse grooves, while the interior is correspondingly 

 divided into a number of compartments by means of a series of septa. 



In addition to the bristles already mentioned, there are often 

 numerous appendages, but these must be distinguished from the 

 more perfect appendages of the arthropods, to be hereafter described ; 

 for while the latter are distinctly jointed to the body, and are 

 themselves made up of parts that are jointed together, the former 

 are mere outgrowths of the body-wall. The digestive and circulatory 

 systems are well developed, as is also the system of water tubes 

 that connect the body-cavity with the exterior, while the body- 

 cavity itself is full of fluid. 



This group of worms is subdivided into two divisions, the many 

 bristled (Polychceta) and the sparsely bristled (Oligochceta) worms. 

 The latter contain the common earthworms and some less known 

 species, while the former include a number of interesting and even 

 beautiful worms, all of which are marine, and many of them among 

 the commonest objects of the sea shore. 



These Polychsetes exhibit a great variety of habit as well as of 

 appearance. Some live in crevices of the rocks or under stones 

 and weeds, or make burrows in the sand or mud of the bed of the 

 sea, and roam about freely at times in search of food. They are 

 continually coming within the ken of the sea-side collector, being 

 revealed by almost every overturned stone near the low-water 

 mark, and are often seen crawling over the wet rocks just left 

 uncovered by the receding tide ; while their burrows are often so 

 numerous that hundreds may be counted in every few square feet. 

 But many are sedentary species, and these are not so generally 

 known to young sea-side naturalists, who frequently observe, arid 

 even preserve, the interesting homes they construct, while less 

 attention is given to the architects that build them. 



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