72 flatwobms, roundwuhms, and rotifees 



Lamp Shells 



These animals are representatives of a class containing 

 several widety different forms. The lamp shells resemble 

 mollusks because their bodies are inclosed in bivalve shells. 

 But the valves are dorsal and A^entral, wliereas tlie valves 

 of the shells of a clam ai'e right and left and similar. In 

 many of these animals, tiie shells are shaped hke 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 reniarkalale 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 ver}' imcertain. It 

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

 are most closely related to the co'lenterates, and so they 

 closel)^ follow in the scale of progression. 



Oire thing is preeminent]}^ 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 will be recalled that part of the 

 life history of certairr worms is passed inside the body of 

 one host and another part of the life liistory ^^'ithin the bod\' 

 of a second and very (Afferent liost. Again, certain worms 

 are alile to live and thrive within the b(i(hes of several 

 different animals. Another noteworth^^ feature of many 

 worms is that the)' are i>arasitic and cause certain malig- 

 nant (hseases wlien present in mair. 



The worms are also well adapted to maintain themselves 

 on the earth. Their ability to hve in different hosts, in 



