Origin of Sexuality 267 



and — cognitic energy discharge to set up. But of this more 

 anon. Frequently and possibly always, the above conjugation 

 changes are ushered in by repeated divisions, in rather rapid 

 succession, of the cells that make up the entire filament. Such 

 is probably associated mth "reduction division" changes that 

 are referred to later.* 



Turning next to the Zoogametse, the component gamete 

 cells are in nearly all cases exactly Hke the asexual swarm- 

 spores. In some cases even (JLJronema, Ctenocladus, etc.) 

 swarmspores are set free, and after a motile existence fix dowTi, 

 without showing any tendency to conjugate. In other cases 

 (Trentepohliay Leptosira) the same vegetative cells of the adult 

 plant give rise to ciliate cells, some of which live through a 

 motile stage and then fix down to form new adult plants, while 

 others conjugate in pairs to form a zygospore from which new 

 growths arise. Again, and very usually, all of the swarm- 

 spores, on being set free from vegetative cells, may live a motile 

 existence and then unite in pairs to form zygospores. 



The above and many similar facts strongly indicate that, 

 in the simpler green algse, ordinary cells of the vegetative 

 thallus may become modified, may separate from it, and form- 

 ing those types of asexual spore that have been distinguished 

 as akinetes, aplanospores, palmellospores, or swarmspores may 

 disseminate, and give origin to like individuals as the parent 

 species. But by the most gradual stages of transition-advance 

 they may become either passive conjugate cells (Conjugatse), 

 or motile conjugate cells (Zoosporeae), which show increasing 

 and increasingly exact stereoenergized attraction for each other 

 by nuclear action and reaction. Such zygospores then differ 

 fundamentally from the asexual spore cells y in that they combine 

 the blended peculiarities of two distinct plants. But as the 

 mature plants, produced by these zygospores, subsequently 

 teach us, and as many facts from the history of higher plants 

 amply verify, the blended parental characters are reduced 

 by about half. 



Another peculiarity of each zygospore cell is that, previous 

 to conjugation, the future conjugate cells display definite 



* Recent studies on Spirogyra and other of the simpler algoe seem fully to 

 confirmlthe above. 



