354 The Animal Kingdom 



Near the reservoir, contractile vacuoles usually form and empty their 

 contents into the reservoir for elimination through the mouth. 



Also near the reservoir is a red pigment spot which is light 

 sensitive. The nucleus is located approximately in the center of the 

 cell. Throughout are many chromatophores containing chlorophyll. 

 These small colored bodies give the green appearance to the animal 

 and are called chloroplasts. The exact appearance and distribution 

 of these chloroplasts varies among the different species. As this 

 chlorophyll is the same material that is found in green plants, it makes 

 possible the synthesis of carbohydrates by the animals. For this rea- 

 son, the phytomastigina are often considered to be plants. Some mem- 



'LAGELLUM 



CYTOSTOUe 

 CYTOPHARYNX 

 EYESPOT 



RESERVOIR 



CONTRACTILE VACUOLE 

 CHLOROPLAST 



NUCLEUS 



ARAMYLUM BODY 

 PELLICLE 



Fig. 111. — Euglena sp. 



bers of the genus Euglena also possess conspicuous whitish structures 

 known as parainyluvi bodies. These are composed of a starchlike ma- 

 terial, parauiyluin, formed by the chloroplast. 



Reproduction is ordinarily by binary longitudinal fission. Sexual 

 reproduction has never been demonstrated with certainty in Euglena. 

 Under unfavorable conditions, Euglena regularly form cysts. At times 

 within these cysts, multiple fission resulting in 16 to 32 individuals 

 occurs. This happens when there is an overabundance of chlorophyll 

 in the cell due to overillumination. The green scum commonly seen 

 on the surface of small ponds often contains large quantities of these 

 encysted Euglena. 



