2 GUIDE TO THE STUDY 



Class INFUSORIA. — Protozoa with an outer cell integument; 

 always ciliated either through life or in the young condition. 



Phylum PLATYHELMINTHES.— The platodes, or flatworms. 

 Bilaterally symmetrical animals devoid of true metameric 

 segmentation and without body cavity. There is no blood- 

 vascular system, but an excretory (water-vascular) system is 

 present. 



Class TREMATODA. — Flukes. Parasitic flatworms without 

 a covering of cilia in the adult state; with a well-developed 

 digestive apparatus typically with a single opening, the mouth, at 

 the anterior end of the body. The sheep liver-fluke is an example. 



Class CES TO DA . — The tapeworms. Endoparasitic flatworms, 

 without cilia and without a digestive cavity; usually becoming 

 segmented as they mature. 



Phylum NEMATHELMINTHES— The roundworms, or 

 threadworms. The body is cylindrical, spindle-shaped, or 

 thread-like, unsegmented, and covered with a thick cuticle; the 

 body cavity (not a true ccelom) is usually spacious. The sexes 

 are usually separate but hermaphroditic species occur. 



Class NEMATODA. — With an alimentary canal but without 

 a proboscis. Both free-living and parasitic forms. 



Order EUNEMATODA. — Alimentary canal typically com- 

 plete and present throughout life. Familiar examples are the 

 ascaris worms, pinworms, hookworms. 



Order GORDIACEA— The so-called "hair-snake." Larval 

 stages parasitic and possessing an alimentary canal. Adults free 

 living, without an alimentary canal. 



Class ACANTHOCEPHALA.— The thorny-headed worms. 

 Lacking alimentary canal; possessing a protrusable proboscis 

 which is covered with many rows of recurved hooks. 



Phylum ANNULATA. — The segmented, or annelid worms. 

 Body composed of similar segments, without jointed legs; 

 alimentary canal with two openings. Only one class contains 

 a considerable number of parasitic forms. 



Class HIRUDINEA. — The leeches. Segments marked 

 externally by secondary rings. Each end of the body is furnished 

 with a sucker. 



Phylum ARTHROPODA. — Crustaceans, mites, ticks, and 

 insects. Bilaterally symmetrical animals in which the body is 

 segmented and bears a pair of jointed appendages on each or 

 some of the segments. Not considered in this course. 



