LIFE HISTORY OF PRORODON GRISEUS. 



GEORGE W. TANNREUTHER, 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF MISSOURI. 



INTRODUCTION. 



Prorodon griseus, a Holotrichous ciliate, is somewhat plastic and 

 variable in shape. When distended it is about two and one half 

 times as long as wide, with its anterior end slightly wider (Figs. 

 1,3). The oral aperture is sub-terminal. The anal pore is at the 

 extreme posterior end. The pharynx is supported by twenty to 

 thirty rod like structures. The contractile vacuole is postero- 

 terminal. The delicate cuticular membrane is finely and closely 

 striate longitudinally. No trichocysts are present. The cilia 

 over the entire body are uniform in length, except at the anterior 

 end where they are slightly longer. These longer cilia are quite 

 active during the process of feeding. A layer of deeply stained 

 bodies are found in the outer border of the ectoplasm. The 

 locomotion of the expanded forms is rather smooth, rapid and 

 straight forward, turning on their long axis. When contracted 

 the motion is chiefly rotary. 



The purpose of the following paper is to give a brief account of 

 the more important features in the life history of P. griseus. 



NATURAL HISTORY. 



The material was collected from small rain pools, more es- 

 pecially from small hog wallows, which is one of their most 

 favorable habitats for rapid growth and multiplication. When 

 present in these small rain pools they are usually found in the 

 surface film in rather large clumps, instead of being distributed 

 throughout the water. When these small rain pools completely 

 dry up abundance of encysted forms are found in the dry sediment 

 on the sides and bottom. Collections were made at regular 

 intervals (including encysted forms from the dry sediment), 

 during the summer months of 1925. The material was placed in 

 finger bowls with tap water added from time to time to counteract 



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