CILIARY MOVEMENT 265 



direction of locomotion, while the other trails behind like a rudder. Many 

 animals possess in addition to large motile cilia others which function as 

 organs of taste or touch, while the ciliated epithelium of Vertebrata no 

 longer serves for bodily locomotory but for other purposes. 



All free-swimming forms possess cilia as locomotory organs, and these 

 either vibrate to and fro or, when large, perform a corkscrew-like action 

 through the water, drawing the organism after them. If the cilia or 

 flagellae are removed or thrown off, the movement of the organism ceases 1 . 

 In the case of minute bacteria, however, the movement of the cilia cannot 

 be directly followed. Even in the case of the swarm-spores of Myxomycetes 

 the free-swimming is due to the cilium and not to any amoeboid movement, 

 although this may be shown at the same time 2 . Most zoospores, however, 

 even when naked, have no power of amoeboid movement, and there seems 

 to be no free-swimming organism devoid of cilia. The latter were recog- 

 nized as locomotory organs by Unger 3 , and Nageli's assumption that they 

 were only passively moved like the oars of a boat was shown by Siebold to 

 be incorrect 4 . The supposition that bacteria moved without the aid of 

 cilia was disproved by the detection of these organs by special methods of 

 fixing and staining 5 . Berthold 6 , however, assumes that the swarm-cells 

 of Erythrotrichia move without the aid of cilia, and it is not impossible 

 that locomotion might be produced by the backward ejection of water 

 absorbed laterally or anteriorly. That certain zoospores such as those of 

 Ckromophyton rosanoffii" 1 should be able to creep on the surface of the 

 water is not surprising, since the surface-tension film is capable of affording 

 the required resistance. 



The forward movement is usually accompanied by one of rotation around 

 the organism's own axis, and the ciliated end is usually first 8 . Under these 

 circumstances the cilia must draw the body onwards, whereas when they 

 are at the hinder end they must push it forwards. The latter is the case 

 in Chytridium vorax 9 and Polyphagns englenae 10 , and possibly it may be 



1 Strong shaking often causes the cilia to be thrown off. Cf. Strasburger, Wirkung des Lichtes 

 u. d. Warme auf Schwarmsporen, 1878, p. 6. If a zoospore is nipped in two during its escape from 

 the zoosporangium, only the ciliated portion shows any free-swimming movement. Cf. Hofmeister, 

 I.e., p. 29. 



2 For instances see Plenge, Verhandl. d. naturh.-med. Vereins in Heidelberg, 1899, N. F., 

 Bd. vi, p. 216; Kolkwitz, Bot. Centralbl., 1897, Bd. LXX, p. 186. On the mechanical distortions 

 of antherozoids cf. Pfeffer, Unters. a. d. bot. Inst. zu Tubingen, 1884, Bd. I, p. 394. 



3 Die Pflanze im Momente der Thierwerdung, 1843, p. 93. 



4 Nageli, Gattungen einzelliger Algen, 1849, P- 22 ! Siebold, Zeitschr. f. wiss. Zoologie, 1849, 

 I, p. 287. 



5 Cf. A. Fischer, 1. c. ; also Migula, 1. c. 



6 Berthold, Protoplasmamechanik, 1886, p. 125. 



7 Woronin, Bot. Ztg., 1880, p. 630. 



8 Nageli, Beitrage z. wiss. Bot., 1880, Heft 2, p. 96. 



9 Strasburger, Die Wirkung des Lichtes u. d. \Varme auf Schwarmsporen, 1878, p. 13. 



10 Nowakowski, Cohn's Beitrage z. Biologie, 1877, Bd. u, p. 208. 



