270 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



The mode of movement of cilia. In the case of typical ciliated epithelium 

 the cilia bend sharply over in one plane and then more slowly return to 

 their original position *. Naturally rotation will in such cases only result 

 when the free-swimming body is appropriately shaped or the cilia specially 

 distributed. It is, however, not known to what extent this type of move- 

 ment occurs in the zoospores of plants. In most cases at least each 

 flagellum appears to curve in successive zones along its length in cork- 

 screw fashion, like a piece of string rotated at one end 2 . Under the 

 microscope the movement appears to be more in one plane, and is carried 

 out either at the apical end or along the whole length of the flagellum. 

 If the movement is slowed by low temperatures or by the viscosity of 

 the medium, the spiral nature of the movement is more prominent, and the 

 photographs of the movement taken under high magnification by Marey 3 

 seem likely to be of great value. In some cases a flagellum may retain 

 a transitory or permanent spiral curvature, while others may describe 

 cone-like revolutions with or without a spiral curving along their lengths. 

 Among the Peridineae, according to Schiitt, one flagellum appears to perform 

 mainly cone-like revolutions, and the other to be thrown into spiral waves. 

 In some cases the character of movement is strongly affected by the 

 external conditions, but in what way the motor mechanism is affected 

 is uncertain. 



When a flagellum is thrown into spiral waves the action is the same 

 as that of a screw fixed in the bow of a boat, a forward movement being 

 produced and the other component of the resolved force tending to produce 

 an axial twisting movement. In both cases, by reversing the motion, the 

 motile organ may push or draw the body onwards, just as in the case of 

 an ordinary screw-steamer, in which, however, the tendency to a rotary 

 movement is negligible. A slight contraction or spiral curvature of the 

 flngellum will not suffice to produce a forward movement, but will produce 

 a lateral one, especially if the flagellum is in contact with a solid body. In 

 this way a jerky locomotion may be produced in many swarm-spores. 



SECTION 59. Gliding Movements. 



These are shown by most Diatoms and Oscillarias and also by certain 

 Desmids, which possess no cilia and have no power of amoeboid movement. 



1 Cf. Engelmann, and also Verworn, I.e.; Bergel, Centralbl. f. Physiol., 1900, Bd. xiv, p. 34. 

 On the spermatozoa of animals cf. Hensen in Hermann's Handbuch d. Physiologic, 1881, Bd. vi, 

 Abth. ii, p. 90. 



1 For details see Biitschli, Die Protozoen, 1880-9, P- 850; Schiitt, Die Peridineen d. Plankton- 

 expedition, 1895, p. 119; Kolkwitz, Bot. Centralbl., 1897, Bd. LXX, p. 185. Cf. also Pfeffer, Studien 

 zur Energetik, 1892, p. 255. 



3 Marey, Compt. rend., 1892, T. cxiv, p. 989. 



