36 MANUAL OF ANIMAL BIOLOGY 



common secretion and serves apparently to hold the cells of the 

 colony together. (W. f. 30, A.) 



The cells in a mature Volvox colony are of two kinds, the body, 

 or somatic cells, and the reproductive, or germ cells. There 

 are many more somatic than reproductive cells. Each somatic 

 cell of Volvox is comparable in its general plan of organization 

 with a single Euglena. However, it should be noted that each Vol- 

 vox cell possesses two flagella, instead of one as in Euglena, and 

 also that from each Volvox cell several cytoplasmic strands are 

 given off which run through the matrix and connect with similar 

 strands from the surrounding cells. Thus there is an anatomical 

 and physiological continuity between the cells of the colony. 

 (W. f. 30, B.) 



Each of these bi-flagellated cells of Volvox is made up of ecto- 

 plasm and endoplasm, and contains a nucleus, contractile vacuole, 

 stigma, and numerous chloroplastids. The cells are similar in 

 structure to various other species of independent, flagellated 

 Protozoa which never form colonies. The structure of the repro- 

 ductive cells is noted below. 



B. Life Processes of Volvox 

 1. Metabolic Processes 



It has been emphasized that the somatic cells of Volvox are 

 balanced structural and functional units, each capable of perform- 

 ing the basic life processes independently. These metabolic 

 activities are performed essentially as in Euglena, which we have 

 considered in the previous chapter. On the whole, Volvox is even 

 more plant-like in its nutrition than Euglena, for it is exclusively 

 holophytic. 



The somatic cells of Volvox are responsible not alone for supply- 

 ing food for their own individual needs, but also for certain needs 

 of the colony as a whole ; such as the formation and upkeep of 

 the intercellular matrix and the nourishment of the reproductive 

 cells of the colony, both of which are to be regarded as the property 

 of the entire colony. On the other hand the function of repro- 

 duction in each colony is assigned to cells specialized for that pur- 

 pose. Thus we have here a beginning of a division of labor between 

 different types of cells, a condition which becomes more and more 

 marked in the ascending scale of animal development. 



