plasts ( chloroleu cites ) which may be disc-hke, ribbons, or stellar 

 plates scattered through the cell or, rarely, radiating from the center. 

 In some forms lens-shaped pyrenoids can be discerned projecting 

 from either surface of the chloroplast. As mentioned above, food 

 reserve is paramylon, a carbohydrate, which may be deposited about 

 the pyrenoid, or it may collect independently in the cytoplasm. The 

 shape of the paramylon grains is specific, and varies greatly among 

 the diflFerent genera and species, and is therefore of taxonomic 

 value. The grains may be minute and numerous rods, a few large 

 sticks, circular plates, or doughnut-shaped rings. The nucleus is 

 usually conspicuous and is centrally located. 



Most members of this family have a single thick flagellum, but 

 a few have 2. The flagella are attached at the anterior end, arising 

 from basal granules and emerging through a canal. Placed anteriorly 

 and laterally is a complex red pigment-spot. 



The shape of cell varies greatly among the genera of the family. 

 It may be fusiform, cylindrical, pyriform, or ovoid, and in cross 

 section it may be either round or much flattened. The cell membrane 

 (the periplast) may be smooth or, more often, variously decorated 

 with spiral striations, rows of granules, or punctae. 



In one genus, Trachelomonas, the protoplast is housed in a test 

 of firm gelatinous material, the flagellum emerging through an apical 

 pore. Although most forms are motile, a few are sedentary, occurring 

 as dendroid colonies. Especially in Euglena certain species are 

 highly metabolic and may use creeping movements, as well as 

 flagella, for locomotion. On the other hand, the cell is quite rigid 

 and maintains a more or less constant shape. 



As mentioned above, the commonly observed method of reproduc- 

 tion is longitudinal cell division (a protozoan attribute). The few 

 cases of sexual reproduction by isogametes or conjugation which 

 have been reported for this family suggest that more life history 

 studies are required. At present there are few observations which 

 indicate other than strictly vegetative reproduction in this group. In 

 Euglena many species- are known to form thick-walled resting cysts 

 which, however, do not lead to multiplication as far as known. Other 

 genera also enter resting stages as an environmental adaptation. 



The family as a whole inhabits shallow water environments, 

 apparently preferring high temperatures and a medium in which 

 there is an optimal concentration of organic matter. 



Key to the Genera 



1. Cells epizoic, attached by gelatinous 



stalks to microfauna Colacium 



1. Cells not epizoic 2 



[388] 



