SWARM-SPORES AND AKTHEROZOIDS, ETC. 



605 



always produce essentially the same kind of movement, shows already that a com- 

 plicated problem of mechanics is here concerned, since we know almost nothing 

 further of the movements of cilia than that they make serpentine or lashing move- 

 ments in the water, from which the motion of the entire body then results. Where 

 numerous cilia move simultaneously in this way, it is even questionable whether their 

 oscillations are always simultaneous and alike in character; in fact it is not 

 necessary to assume this in the case of the production of the ordinary rotating move- 

 ment of swarmers, since we know from Thuret's investigations that the relatively 

 large oospheres of the Fucaceae are set in rotating motion by the convulsive 

 movements of the numerous spermatozoa cUnging to its periphery — this rotation 

 evidently results from the very irregular strokes of these extremely minute (in 

 comparison with the oosphere itself) bodies. 



Among the most significant mechanical points is the always considerable size of 

 the swarm-spores in comparison with the extreme minuteness of the motile organs, 



FIG. ^i,i.~Stefhanosphaera pluvialis (after Colin and Wichura). /resting spore; It—Vin swarm-spores 

 produced by the division of /. VIII—X tlie family produced by division of one swarm-spore ; XI a mature 

 family rotating ; .T//— -.IT/^microspores produced by division of the cells of -l'/. 



the cilia. Of course their work is essentially facilitated by the fact that the swarm- 

 spore possesses nearly the same specific gravity as the water; but it is obvious that it 

 must always be a little heavier, owing to the specifically heavier proteid substance 

 of the protoplasm. Dead sw^rm-spores therefore always sink to the bottom. The 

 swimming itself, so far as it only concerns suspension in the water, is thus work 

 done by the cilia, but the friction which must necessarily take place during the 

 rotation and progressive motion at the surfaces of the swarm-spore is perhaps 

 greater even than this. From all that is known so far we must probably ascribe 

 to the cilia also the irritability of which we shall consider the different manifestations 

 later on. 



The form of movement which all the objects here under consideration exhibit con- 

 sists in that in the first place they rotate on their own longitudinal axes, usually swim- 

 ming forwards at the same time; the movement is thus approximately that of a planet 

 with its diurnal rotation and simultaneous flight away into space, or that of a shot 



