84 



PROTOZOA 



the tip by means of which the suctorian captures other protozoans and 

 passes them back to the mouth to be taken into the body. 



111. General Facts. — Protozoa vary in size from minute blood para- 

 sites which are invisible or barely visible to the highest powers of the 

 microscope to a gregarine, Porospora, which lives in the alimentary canal 

 of the lobster and which may be 17 mm., or ^3 inch, in length. Most of 



Nucleus 



B 



Nucleus 



Nucleus 



Fig. 30. — Some forni.s of Infusoria. .4, a species of Podophyra. {After Butschli, 

 "Klassen und Ordnunycii das Ticrreichs.") To illustrate the Suctoria. Highly 

 magnified. B, Opalina ranarum Purkinje. {From Ke7it, "A Mamial of the Infusoria" 

 after Zeller.) An infusorian parasite of frogs. X 80. C, a species of Vortictlla. {Modi- 

 fied from Hegner, ''College Zoology," after Shipley and Machridc.) Showing a portion of the 

 attachment stalk coiled. Highly magnified. D, Stcntor polymorphus Mi'illcr. {From 

 Kent.) X 60. Attached individual. E, Balantidium coli Malmstcn. {From Thomson 

 and Robertson, "Protozoology") X 400. F, Stylonychiamytil us Ehrenherg. {From Kent.) 

 X 100. {C by the courtesy of The Macmillan Compa7iy; E by that of William Wood & 

 Company.) 



them are not visible to the unaided eye. The shapes of Protozoa are 

 also exceedingly varied. 



The cytoplasm of protozoans usually appears alveolar and is divided 

 into ectoplasm and endoplasm. Sometimes the nucleus is scattered 

 throughout the cell in small portions known as chromidia, when it is 

 called a distributed nucleus. We have already noted that in certain 

 cases there are two kinds of nuclei, the macronucleus and the micronu- 



