POLYTOMELLA CITRI, SP. NOV. 217 



several of the division stages figured in this paper (Figs. 13-15). 

 Sections of cysts showed a centriole very clearly. 



In the active forms an indication of rhizoplasts connecting the 

 basal granules with the nucleus was seen in a few cases (Figs. 20 

 and 24). This, how r ever must remain purely tentative until more 

 evidence can be produced. There is no doubt as to the presence 

 of this structure in the cyst just previous to excystment (Figs. 

 38-40). Whether it degenerates after excystment or merely 

 was not demonstrated because of faulty technique, or for other 

 reasons, cannot be decided. 



Scattered through the cytoplasm of the active form there are 

 sometimes seen a few very basiphilic granules. These stain even 

 darker with iron-alum-haematoxylin than does the nuclear chro- 

 matin, and also give the typical reaction with Bonney's triple 

 stain and methyl green. They increase to such an extent in the 

 cyst that during part of that stage they effectually obscure the 

 entire contents of the cell. For reasons which will be discussed 

 later these are termed metachromatic granules. 



Seven individuals with two nuclei have been seen. They 

 probably represent cases where fission was prevented, by some 

 unknown reason, from following mitosis. 



When the resting condition is entered the flagellates cease 

 movement, lose their flagella, round up into a perfect sphere and 

 secrete an extremely thick wall (Fig. 26). From this early 

 spherical stage they pass into an indefinitely wrinkled condition, 

 which must result from drying of the cell contents (Figs. 28 and 

 29). A gradual disappearance of the starch bodies can be traced 

 and correlated with the wrinkling of the cyst. Chloro-zinc- 

 iodide and sulphuric acid followed by iodine both indicate the 

 wall to be composed of cellulose. 



LIFE HISTORY. 



So far as could be determined the life history consists of two 

 phases, (i) active life and (2) rest and reorganization through 

 encystment. During the time of activity Polytomella reproduces 

 by means of longitudinal fission. No multiplication whatever 

 takes place during the period of rest. This is well established 

 since hundreds of stained specimens have been examined and 



