POLYTOMELLA CITRI, SP. NOV. 215 



dimensions are 12 by 8 micra. Although the body of living 

 individuals is usually pear-shaped, the form can readily be 

 changed. Thus we find some whose width is greater than their 

 length, others with their posterior ends split into two or more 

 pointed processes (Figs. 2, 3 and 4). In the latter case a groove 

 extends forward for some distance from the notch between these 

 processes. An optical cross-section of the typical form would be 

 circular. 



The cell is enclosed in a very thin pellicle. This covering is not 

 visible in life and it divides with the body at fission. It is also to 

 be noticed that it is not sufficiently rigid to prevent considerable 

 changes of shape (Figs. 2 to 4). However, its presence can be 

 demonstrated by dissolving the contents of the cell with dilute 

 NaOH. When this is done the pellicle can be seen, providing the 

 light is cut very low. In some cases plasmolysis causes the 

 protoplasm to shrink away from the wall, thereby serving as a 

 demonstration of its existence, but it requires very careful 

 manipulation. The composition of this covering could not be 

 determined, but since the heavy wall which develops around the 

 cyst was found to be cellulose it is presumed that this has the 

 same chemical constitution. 



At the center of the anterior end are two very noticeable basal 

 granules from which arise four equal flagella. These are slightly 

 shorter than the body and do not taper at all, being as large at the 

 free end as at the point of insertion. The two pairs of flagella are 

 well separated in the living organism by a small cytoplasmic 

 protuberance which extends forward between the basal granules 

 (Fig. i). This prominence is never preserved after fixation. 



The two contractile vacuoles are located at the anterior end. 

 They pulsate alternately. 



The spherical nucleus is about 3 micra in diameter and is 

 situated at any point along the long axis of the cell from the 

 posterior fourth to the anterior fourth. All of the chromatin is 

 concentrated in a central sphere, the karyosome. This body is 

 anchored to the nuclear membrane by an indefinite number of 

 achromatic strands. Six is the greatest number of these supports 

 that have been seen, four the least. Aside from the strands .the 

 space between the karyosome and membrane is optically empty. 



