56 



ORGANISMS OF ONE CELL 



mosis, as must be the case in many protozoa in which no 

 contractile vacuole can be found. 



Chilomonas may frequently be seen in pairs swimming 

 along side by side; these are sister cells not yet fully divided 

 and they have originated by the longitudinal division of the 

 cell. Reproduction thus is of the simplest type, the nucleus 

 always dividing first, then the cell body, while new flagella 



FIG. 22. A flagellated protozoon, Copromonas subtilis. A, A normal adult cell 

 before division; B, two individuals in conjugation; C, D, E, and F, later stages in 

 the fusion of cells and nuclei, and formation of protective cyst. (From Dobell.) 



are formed as outgrowths. It is not known how these originate 

 in Chilomonas but from analogy with other forms of flagellates 

 where the process is known, two of the four at least must be 

 new growths ; in some cases the old flagella are withdrawn and 

 new ones are formed; in other cases one of the two flagella goes 

 to each daughter cell. 



