306 GEORGE W. TANNREUTHER. 



Or again the macro-nucleus elongates more and more until the 

 halves are connected by a mere thread and finally constricts when 

 the separation of the cytoplasm in the formation of the daughter 

 cells is complete (Fig. 5). 



The new pharynx with its rod-like structures and the new 

 contractile vacuole are formed before the nuclei divide. The 

 entire process of binary fission requires about one and a half hours 

 for completion. Binary fission occurs at any period in the life 

 cycle of the animal. But the greater number of divisions were 

 found to occur after conjugation during the active feeding stage. 

 But if the conjugants encyst immediately after separation, due to 

 adverse conditions, binary fission occurs within the cyst (Fig. 2d) 



NUTRITION. 



The direct observation of the feeding process in Prorodon is 

 rather difficult, due to the rotary motion of the individuals when 

 stationary or when swimming. The animal feeds chiefly upon 

 bacteria and other small unicellular organisms. The origin, 

 formation and fate of the food vacuoles is comparable to that of 

 other ciliates where it is more easily followed. The animal at 

 times is so gorged with food vacuoles, that a cytological study is 

 impossible, since the body appears as a mass of indistinctly 

 stained objects. Many of the individuals during feeding increase 

 from two to three times in volume before binary fission occurs. 

 This increase in size however, is due more to expansion than 

 growth. The large mass of food vacuoles within the organism 

 undergoes a constant movement in one direction for short 

 intervals and then moves to and fro as a sort of churning. This 

 constant circulation of the food vacuoles no doubt is greatly 

 facilitated by the constant rotary motion of the organism. The 

 food within the vacuoles undergoes a rapid digestion or lique- 

 faction giving the vacuoles a clear content, which soon passes out 

 into the cytoplasm. The food vacuoles as a rule are quite large, 

 due to the great amount of fluid surrounding the food. Thus 

 giving the appearance of a vesicle with a clear border and a dark 

 center. The vacuoles finally collapse and the indigestible 

 particles are voided at the posterior end through the anal 

 pore. 



