1 66 



COLLEGE ZOOLOGY 



off from the "neck." Archigetes (Fig. no) differs from other 

 tapeworms both in structure and habit ; it has only one proglot- 

 tis, and lives in the ccelom of an annelid, Tubifex. 



A few Cestodes and their hosts are given in Table VIII (from 

 the Cambridge Natural History). 



TABLE VIII 



THE LIFE-HISTORIES OF A FEW CESTODES 



5. Flatworms in General 



Definition. — Phylum Platyhelminthes. — Flatworms. — 

 Triploblastic animals; bilaterally symmetrical; single gastro- 

 vascular cavity; no anus; presence of ccelom doubtful. 



The flatworms are more highly organized than the Ccelen- 

 terata or Ctenophora and are distinctly triploblastic. The 

 middle germ-layer, the mesoderm, which is well developed in flat- 

 worms, is connected with several important systems of organs, 

 since it is from this layer that the muscles, the -excretory system, 

 and the reproductive ducts originate. The development of these 



