ALTERNATION OF GENERATIONS 241 



continuous cell-multiples, which may be free or may remain 

 attached to each other, the alternation may attract atten- 

 tion. For the arrest accompanying Continuity here prevents 

 sexless or intermediate cells, or their multiples, from ever 

 becoming sexual, and these thus remain in lasting contrast 

 with the ultimately appearing sexual forms. 



Regarding, then, Alternation of Generations as essen- 

 tially Alternation of Cycle-stages, we might summarise the 

 ways in which it is exhibited in the ascending Individual 

 scale. 



I. The Discontinuously Multicellular Individual. — Fig. 79 

 represents diagrammatically such an Individual developing 

 as so many sexless unicellular organisms, each an evanescent 

 intermediate stage in the cycle, and drawn as a number 

 of " o's." When this Individual is theoretically complete 

 it is composed of nothing but gametes (x, x). 



ooooo xxxxxxx 



ooooo xxxxxxx 



becomes 

 ooooo xxxxxxx 



ooooo xxxxxxx plus 



Fig. 79. 



For example, an examination of the blood of a person 

 affected with malaria will, in the early days, reveal only 

 amoeboid or " sexless " forms of the parasite ; but at a later 

 date gametes or sexual forms may be discovered. The 

 former are stages on the road to gamete production, and 

 become gametes in their future product. Discontinuity is 



\m i «. i " l - 1 - l 



Fig. 80. — Diagram of filamentous growth (as in Spirogyra), 

 exhibiting cellular alternation of cycle-stages. 



here the factor which, other things being equal, allows this 

 to occur. When the Individual is truly complete, the inter- 

 mediate or " sexless " stages should all have vanished, 

 and no alternation would be observable. 



II. The Filamentous Individual. — Here there is the same 



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