178 THE SEA SHORE 



It is very interesting to observe some of the general differences 

 between the roving and the sedentary species differences which 

 illustrate the principle of adaptation of structure to habit. The 

 roving species are provided with a lobe that overhangs the mouth, 

 bearing feelers and eyes, and are thus enabled to seek out any 

 desired path and to search for their food. They are provided with 

 bristles and other appendages by means of which they can travel 

 freely over the suri'aces of solid objects, and are able to swim well 

 either by undulations of the body, or by fringed appendages, or 

 both. The carnivorous species, too, are provided with strong, horny 

 jaws, and sharp, curved teeth, by means of which they can capture 

 and hold their prey. The sedentary species, on the other hand, 

 unable to move about in search of food, are supplied with a number 

 of appendages by means of which they can set up water currents 

 towards their mouths, and which also serve the purpose of special 



FIG. 117. Arenicola piscatorum 



breathing organs, and, having no means of pursuing and devouring 

 animals of any size, they do not possess the horny jaws and curved 

 teeth so common in the rovers. Their eyes, too, are less perfectly 

 developed, and the tactile proboscis of their free-moving relatives 

 is absent. 



Of the roving worms, perhaps, the Lugworm or Sandworm 

 (Arenicola piscatorum) is the best known. Its burrows may be 

 seen on almost every low sandy or muddy shore, and, being so 

 highly valued as a bait, its general appearance is well known to 

 all professional and amateur sea fishers. It reaches a length of 

 eight inches or more, and varies in colour according to the sand 

 or mud in which it lives. The segments of this worm are very 

 different in structure in different parts of the body. Those in the 

 front of the body have a few tufts of bristles arranged in pairs, 

 while the middle portion of the body has large brush-like tufts 

 of filamentous gills placed rather close together ; and the hindmost 



