122 D. H. WENRICH 



THE VEGETATIVE INDIVIDUALS 

 A. Form 



Both in the Uving and the fixed condition the body of this 

 species of Trichomonas is rather fusiform, with a length of from 

 one and a half to two times the greatest width. There is some 

 tendency for the so-called dorsal side to be more convex than 

 the opposite, somewhat flattened, ventral side. In the free- 

 living condition the region of greatest width is usually near the 

 middle, but the flexibility of the pellicle permits a variety of 

 shapes, especially when the animals are creeping or forcing their 

 way through the coecal debris. Then the body may change 

 shape rapidly and some of the variations are to be seen in the 

 fixed material. For example, figure 7 shows an animal with 

 the anterior end much more pointed than the one in figure 8. 

 Figures 8 and 17 show animals with the greatest width at the 

 posterior end instead of in the middle, as is more common. 



Adverse conditions, such as lowered temperature, changes in 

 the constitution of the surrounding fluid, or desiccation, often 

 lead to considerable changes in form, the most comimon modifi- 

 cation being the rounded-up condition (figs. 11, 13, and 15). 

 The rounded form also seems to be characteristically assumed 

 during the process of division (figs. 20 to 30). When confined 

 in cramped quarters the form changes are exceedingly various. 



In free-swimming animals the undulating membrane is spirally 

 arranged on the surface of the body, and they rotate on the long 

 axis, without any appreciable changes in diameter. On the 

 other hand, fixed and stained individuals often give the impression 

 of being flattened and of lying on one side with the undulating 

 membrane at one edge, as seen, for example, in figures 1 to 4. 

 In those specimens showing the spiral arrangement of the un- 

 dulating membrane and accompanying structures, it is seen that 

 the direction of the spiral is from the left over to the right, as 

 shown in figures 5 and 17 and in text figure A. 



