IV. VOLVOX 



Volvox is a colonial, fresh-water organism, the body of which 

 consists of a great number of independent flagellated cells. These 

 cells are essentially similar to Euglena in structure, and like the 

 latter have the holophytic type of nutrition. The presence of 

 chlorophyll, just as in Euglena, makes the exact relationships of 

 this organism a doubtful question. Volvox is classified with the 

 unicellular, flagellated animals as a Protozoon or in the lowest order 

 of Green Algae as a primitive plant form. Our main point of inter- 

 est, however, in connection with Volvox lies in the fact that it is a 

 primitive multicellular organism in which each individual consists 

 of a great number of cellular units permanently associated to form 

 a colony. In a Volvox colony each cell is a balanced structural 

 and physiological unit capable of carrying on the necessary life 

 processes independently of the other cells of the colony, except that 

 certain cells may be specialized for reproduction. 



In the higher multicellular plants and animals — all of which, 

 in the final analysis, are essentially colonies of cells — there is an 

 ever-increasing amount of cell specialization as we ascend in the 

 scale of development. Along with this has come a division of labor 

 between the cells, so that in these organisms the cells have become 

 both structurally and functionally specialized to such an extent 

 that they are capable of performing only certain of the life processes 

 which are necessary for the welfare of the organism as a whole. 

 Thus, for example, the functions of nutrition, irritability, move- 

 ment, and numerous others are carried out in these higher types of 

 organisms by groups of cells which are differentiated and adapted 

 for their own particular work. 



A. Structure of Volvox 



Volvox is large enough to be seen with the naked eye. It ap- 

 pears as a small, green, hollow sphere, the wall of which is com- 

 posed of some ten or twelve thousand microscopic, flagellated, 

 chlorophyll-bearing cells, together with a transparent, gelatinous, 

 intercellular material, the matrix. The latter is formed as a 



34 



