THE FILAMENTOUS INDIVIDUAL 53 



As an example of a Filamentous Individual we will take 

 the Alga, Spirogyra. 



Spirogyra. 



This freshwater Alga grows as a long green thread or 

 filament of cells in single series, but although these are united 

 in continuity, they are virtually independent organisms. 

 The only function the cells may be said to perform for the 

 general good is that of maintaining continuity ; apart from 

 this, each cell lives for itself ; thus the Continuity of Spirogyra 

 is not comparable with that of organisms whose cells are 

 truly interdependent, each living for the good of the whole 

 cell-mass. 



Theoretically, each cell of the Spirogyra filament should 



fc. 



Fig. 6. — Proximal cell-arrest in Filamentous development. 



become sexual in its descendants, or, as we might put it, 

 the theoretically complete Individual should be, as in the case 

 of the Discontinuous Multicellular Individual, an immense 

 number of gametes. Nevertheless, Continuity prevents the 

 cells from carrying on the growth-cycle simultaneously. 

 Temporary cell-arrest is exhibited. This arrest is indicated 

 by the appearance of gametes at varying intervals in the 

 length of the filament, for if each cell as it was produced 

 grew to divide at one uniform rate there would be more or 

 less simultaneous gamete-production ; every cell being at 

 a given moment at the same distance from the end of the 

 cycle. On what system, then, does cell multiplication take 

 place ? A definite answer cannot be given to this question, 

 but there are reasons for supposing that the Spirogyra filament 

 develops on a plan somewhat like that illustrated in Fig. 6. 



