360 Animal Biology 



Reproduction. — Binary longitudinal fission occurs by a splitting of the 

 body at the anterior end which continues posteriorly until completed. 

 The nucleus, chloroplasts, etc., also divide. Occasionally, a Euglena 

 throws off its flagellum and surrounds itself with a thick, gelatinous cyst 

 (Gr. kystis, bag) to resist drying conditions. Sometimes longitudinal 

 fission may occur while the animal is encysted and new flagella are 

 formed. As many as thirty-two Euglenae in one cyst have been observed. 

 When proper conditions are encountered, the cyst breaks and the Eu- 

 glenae emerge to assume an active life again. 



VOLVOX 



Volvox (vol' vox) (Gr. volvo, turn) is a colonial protozoan in which 

 thousands of body (somatic) cells are associated to form a hollow, water- 

 filled, globe-shaped colony. A common species is V. globator (L. globus^ 

 ball). Because Volvox contains certain plantlike characteristics (chloro- 

 phyll, cellulose), it might be considered as a plant-animal (Figs. 174 and 

 175). 



Integument. — The body wall consists of cellulose, a material common 

 in plants. A gelatinous matrix (mat' riks) (L. mater, mother) serves as 

 an intercellular substance to bind adjacent cells together. The cells are 

 arranged in a single layer, and many of them bear two flagella. 



Motion and Locomotion. — Most of the body cells bear two flagella 

 whose lashing movements give the colony a rotating locomotion. The 

 male sperm are also supplied with flagella. 



Ingestion and Digestion. — Most of the body or somatic cells (so- 

 mat' ik) (Gr. soma, body) contain chlorophyll by means of which car- 

 bon dioxide and water may be combined to form foods by photosynthesis 

 in the presence of energy-supplying light. There is no cytostome so solid 

 foods cannot be ingested. Chlorophyll is borne in chloroplasts. 



Circulation. — There is no special circulatory equipment, but materials 

 are probably circulated by the flowing of the cytoplasm (cyclosis). 



Respiration. — Respiration probably takes place through the general 

 body surface. Possibly some of the carbon dioxide is used in photosyn- 

 thesis, and some of the oxygen from photosynthesis is used for its various 

 activities. 



Excretion. — Most of the body cells contain a contractile vacuole which 

 collects wastes and throws them to the outside. Since the colony is only 

 one cell in thickness, possibly each cell can easily rid itself of its waste 

 materials. 



