SPECIAL MORPHOLOGY AND TAXONOMY OF INFUSORIA 401 



Family 8. Hypocomidae.— The one genus in this family, Hypo- 

 coma, differs from all other Siictoria in having permanent cilia and 

 a definite ventral surface bearing one tentacle in addition to the cilia. 

 This form if not a degenerate holotrich may be interpreted as a 

 stage of arrested development of a ciliated embryo which has 

 developed a suctorial tentacle and has become permanent. An 

 earlier interpretation explained it as a transitional form between 

 the ciliates and the Suctoria. 



KEY TO GENERA OF INFUSORIA. 



With simple or compound cilia during vege- 

 tative life Class 1 . Ciliata 



Adults with tentacles ; cilia only during devel- 

 opment Class 2. Suctoria 



Class I. CILIATA, Hutschli. 



1. Body with adoral zone of membranelles. . . 2 



Body without adoral zone Order 1. Holotrichida 



2. Adoral zone winds to the left 3 



Adoral zone winds to the right . . . Order 5. Peritrichida 



3. Motile organs confined to ventral surface 



Order 4. Hypotrichida 

 Motile organs variously distributed .... 4 



4. Body covered with cilia Order 2. Heterotrichida . 



Cilia on body absent or much reduced 



Order 3. Oligotrichida 



Order I. HOLOTRICHIDA, Stein. 



1. Moutliless (astomatous) forms; parasitic 



Sub-order 1. Astomina 

 With mouth; parasitic or free-living 2 



2. Mouths usualh' closed; oral membranes 



absent Sub-order 2. Gymnostomixa 



Mouths usually opened; oral membranes 

 present Sub-order 3. Trichostomina 



Sub-order 1. Astomina, Cepede. 



1 . With macronuclei and micronuclei 2 



Nuclei two or more but all alike. .Group 1. {Opalinidce) 



2. Parasites of digestive tract; various animals 



Group 2. 



Parasites of coelomic cavity Group 3. 



Parasites of branchial cavity, uterus, 



gonads, etc Group J,. 



Group 1 . Family Opalinid.e 



1. Form cylindrical; circular in cross-section. 2 

 Flattened forms; ellipsoidal in cross-section 3 



2. With two similar nuclei Genus Protodpalina 



With many similar nuclei Genus Cepedea 



3. With two similar nuclei Genus ZeUeriella 



With many similar nuclei Genus Opalina 



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