72 flatwoems, roundworms, and rotifers 



Lamp Shells 



These animals are representatives of a class containing 

 several widely different forms. The lamp shells resemble 

 moUusks because their bodies are inclosed in bivalve shells. 

 But the valves are dorsal and ventral, whereas the valves 

 of the shells of a clam are right and left and similar. In 

 many of these animals, the shells are shaped like an old 

 Roman lamp, hence the name. 



They are all marine and many of them are attached to 

 some object in the sea by a fleshy stalk, or peduncle. They 

 are remarkable for the fact that their shells are found in 

 nearly the oldest rocks in the earth and are very little 

 different from the forms existing to-day. 



Relationships and noteworthy features of the worms. — 

 The relationships of these animals are very uncertain. It 

 is thought, with reason, that the foregoing groups of worms 

 are most closely related to the coelenterates, and so they 

 closely follow in the scale of progression. 



One thing is preeminently characteristic of some of the 

 worms, namely, the strange and remarkable changes they 

 pass through in completing their life history, notably the 

 liver fluke. Moreover, it wiU be recalled that part of the 

 life history of certain worms is passed inside the body of 

 one host and another part of the hfe history within the body 

 of a second and very different host. Again, certain worms 

 are able to live and thrive within the bodies of several 

 different animals. Another noteworthy feature of many 

 worms is that they are parasitic and cause certain maUg- 

 nant diseases when present in man. 



The worms are also well adapted to maintain themselves 

 on the earth. Their ability to live ia different hosts, in 



