EDMONDSON — PROTOZOA OF IOWA. 37 



green in color. Flagellum single, inserted in a notch-like exca- 

 vation on the anterior border. Eye-spot usually present. 



EUGLENA VIRIDIS Ehr. 



Body usually rounded anteriorly, with a colorless tail-like pos- 

 terior prolongation, surface smooth. Nucleus central, contractile 

 vesicle and eye-spot in the anterior region. 



Eength of body, 50-75 microns. (Fig. 5r, PI. VIII.) 



This specimen is one of the most common forms of the class to 

 be found in fresh and stagnant waters. That Euglciia viridis 

 possesses a distinct oral aperture has long been demonstrated and 

 although the organism may depend in part upon the chlorophyl 

 which it usually contains, there is no doubt but that it may at 

 any time ingest organic substances and during periods, when 

 the chlorophyl is lost, may exist entirely upon food obtained in 

 this manner. 



There may be periods of more or less duration during which 

 no chlorophyl or pigment spots are present, and at the same time 

 the activity of the organism is not apparently lessened. 



That Eiiglena viridis is extremely sensitive to the various forms 

 of stimuli and changing conditions, may be readily observed in 

 the laboratory. The organism is repelled by cold and darkness, 

 attracted by heat and light. A few hours in total darkness has 

 proved sufficient to cause the species to become encysted. Other 

 conditions even in a state of nature frequently cause the chloro- 

 phyl to break down into pigments of various colors. Starch-like 

 bodies are often contained within the endoplasm. 



Reproduction takes place by longitudinal fission and also by 

 spore formation. 



Figure 51, Plate VIII, illustrates a normal individual of the 

 species. Often found on the surface of stagnant water in masses 

 visible to the naked eye. Also found commonly among algae. 



EUGLENA SPIROGYRA Ehr. 



Body elongate, cylindrical, posterior extremit}' terminating in 

 a pointed, tail-like prolongation, endoplasm usually bright green, 

 the periphery covered by oblique rows of minute, bead -like 

 elevations. Nucleits centrally located on either side of which is 

 usually an elongated elliptical starch-like body, contractile vesi- 



