94 



ONE-CELLED ANIMALS— PHYLUM PROTOZOA 



classified as a plant. This state of affairs is indicative of the thin line 

 of distinction which separates the two great kingdoms of living things 

 in their elemental forms. It is true that euglena has chlorophyll and 

 can manufacture its food, as do most plants ; but further study shows 

 that it can live in the dark by absorption of nutritents that are present 

 in the water. This indicates the presence of digestive enzymes which 

 are animal-like in nature. Since green plants do not typically have 

 such enzymes, euglena may be considered as an animal that has de- 

 veloped the plant-like characteristic of chlorophyll. Also, euglena can 





Courtesy General Biological Supply House 



Fig. 7.6. Trypanosoma gambiense in blood. Sufficient numbers of these in the blood 

 cause the disease of African sleeping sickness. 



sometimes be seen moving about by "inching" along somewhat like a 

 measuring worm. This type of movement (euglenoid movement) is 

 animal-like in its nature rather than plant-like. 



Euglena has a red eyespot near the flagellum. This is sensitive to 

 light and thus represents a localization of the light-sensitive portion of 

 the cell. By use of this sensory body the euglena is able to perceive 

 and move to areas where the amount of light is best for photosynthesis. 

 This can be very dramatically demonstrated if a culture jar containing 

 euglena is covered with black paper except for a small hole cut in the 

 paper. When the paper is removed there will be a green spot in the 

 culture where the hole in the paper allowed light to come through. 



