24 



BIOLOGY OF THE PROTOZOA 



only 2| protozoon cysts per cubic millimeter of air and that these are 

 limited to 13 species and represent the same types for the most part, 

 as those listed by Woodruff. Protozoa are very apt to stick to 

 solid substances when they encyst and are carried, in the dried state, 

 with such substances, which accounts in part for the appearance of 

 Protozoa in all kinds of infusions. Similar adhering cysts may be 

 carried from place to place by birds and other flying creatures or 

 In' land animals thus helping to maintain a common type of proto- 



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Fig. 5. — Types of Protozoan cysts. A, oi Ochromonas s^p; B, oi Hydrurus foetidus; 

 C, of Podophrya fixa; D, of Euglypha alveulata; E, of Chromuiina pascheri; F, of Vahl- 

 kampfia Umax. {A, B, E, after Kiihn; C, D, F., after Calkins.) 



zoan fauna in pools and casual waters. Some forms to which 

 Lauterborn (1901) has applied the term "sapropelic fauna," appear 

 to be able to live without free oxygen. Thus Frontonia leucas, 

 Prorodo7i oinwi, Spirosfomum amhigimm, Pchrmyxa pahfstris, P. 

 hinucleata, etc., which usually live in relatively clear waters, may 

 also live in the sulphurous medium of putrefying vegetable and 

 animal matter, while certain species of ciliates of fantastic form, 

 seem to require this peculiar habitat for their vital activities 



