256 Causes and Course of Organic Evolution 



is highly energotactic. But each spore is, in higher examples, 

 often provided with a red sensitive eye-spot, that is placed 

 below or near the cilia, more rarely at the rounded end as in 

 Leptosira, when the position indicates the rounded end as 

 that for attraction and coming together of the swarm-cells, 

 if these are to copulate as sex-cells. 



As preliminary to the larger question of sex-cell origin, we 

 may next inquire whether any pronounced cytological changes 

 occur when vegetative or resting cells become changed into 

 swarm cells or spores. The knowledge that would enable 

 us to give a satisfactory reply is still extremely limited. But 

 a few carefully described cases seem at least indicative. Thus 

 Wille (100: 62) in condensing Klebs's original account gives 

 the foUo^ang for Scotinosphcera, one of the Protococcacese : 



"In S. the swarmspores are formed from perennating (or 

 winter) cells in May and June, as soon as they reach fresh 

 water. The differentiation of the protoplasm appears then 

 clearly, and the entire protoplasm is finely granular. The 

 individual masses then separate gradually more and more 

 from each other, while they become shrunken together, and 

 between them appear small red areas. The masses condense 

 increasingly under contraction, and a red coloring matter 

 appears in ever greater quantity around. Finally a dark 

 blue-green protoplasmic ball is formed which lies in the red 

 granular mass. This now begins to split through successive 

 cell-divisions, and the red granular mass is again absorbed. 

 After 12-14 divisions the swarmspores ripen, and by swelling 

 of the parent wall they become free." 



What happens physico-chemically while these modifications 

 proceed we cannot as yet say, though a profound rearrange- 

 ment of the entire bio-cognitic substance is suggested. 



Whether maturing sex-cells have been derived from ordinary 

 vegetative and passive cells, as in desmids and higher Con- 

 jugatse, or first developed as swarmspores, as is most widely 

 true for groups of green algse, it invariably seems that some 

 l)hysico-chemical change so occurs in the maturing or matured 

 gametes that they show marked attraction for each other. 



