PHYLUM PROTOZOA 79 



i. Protozoa. Learn to distinguish Protozoa from other microscopic animals. 

 They are recognizable by absence of cell walls and absence of organs, their bodies 

 having a granular structureless appearance. The common Protozoa met with 

 in cultures besides Paramecium are: 



a) Vorticella: This relatively small protozoan is readily recognized by its 

 bell-shaped body and the slender stalk arising from the top of the bell and per- 

 manently attaching the animal to other objects in the culture. The stalk is 

 contractile; in fact it contains a spiral muscle, which on shortening draws the 

 stalk into the shape of a spiral spring. We thus see that muscular fibrils can be 

 differentiated even within the limits of a single cell. The free end of the bell 

 bears a circle of swiftly vibrating cilia, and a large opening to the gullet. Look 

 for food vacuoles, contractile vacuoles, etc. The horseshoe-shaped macronucleus 

 can be seen only after staining with aceto-carmine. 



b] Stentor: This animal is a large trumpet-shaped form, usually attached 

 to objects. The broad end bears a circle of large cilia, and a conspicuous spiral 

 gullet. The ectosarc is striped. The stripes are muscular fibrils which enable 

 the Stentor to undergo considerable changes of shape. The macronucleus 

 resembles a string of beads and is generally a conspicuous object. 



c} Hypotrichous dilates: This group of ciliates is easily distinguished by a 

 jerky darting method of locomotion, and the possession of large cilia which are 

 used as legs for creeping over objects. These cilia are really fused bundles of 

 .cilia, usually called cirri, and it. is a remarkable fact that each one of them can 

 be moved independently. Look for gullet, contractile vacuole, etc. The 

 nucleus cannot be seen without staining. Use aceto-carmine. Common forms 

 are Euplotes, Stylonichia, Oxytricha. 



d) Other ciliates: Ciliates are the commonest Protozoa, and a great variety 

 may be expected in cultures. Frontonia is similar to Paramecium, but larger 

 and more oval in form; Didinium may be recognized from Hegner's Fig. 26 

 (p. 63) ; Spirostomum is a long, slender, cigar-shaped ciliate with oblique muscle 

 stripes; Lacrymaria is spindle-shaped with a very long, slender, mobile "neck"; 

 Dileptus is a large form with a short contractile neck; Colpoda is a small oval 

 type with a marked indentation near the anterior end; Coleps is distinguished 

 by an armor of small squarish plates; Halteria is a quite small, nearly spher- 

 ical ciliate, moving by swift darts. These are the forms which we commonly 

 get in cultures "seeded" from natural waters in the Chicago region, but many 

 others may be expected. 



e) Heliozoa, or sun animalcules: Spherical protozoans with stiff radiating 

 pseudopodia and bubbly protoplasm are not infrequently found. They are 

 related to Amoeba. Actinophrys, small, and Actinosphaerium, quite large, are 

 the common kinds. 



/) Amoeboid organisms: The only other common protozoan, similar to 

 Amoeba, is Arcella. This animal resembles Amoeba in all essential respects 



