Physiology 491 



lates. Perhaps the most plausible mechanism is that suggested by Lowndes 

 (333, 334, 335), whose data indicate that the basic function of the flag- 

 ellum, at least in uniflagellate species, is to produce rotation of the or- 

 ganism on its major axis as well as gyration about an axis which marks 

 the general direction of locomotion. In flagellar activity, waves pass 

 spirally along the flagellum with increasing amplitude from base to tip, 

 producing two distinct components of force. The resultant of these two 

 components, acting on the anterior end of the flagellate, causes both ro- 

 tation and gyration which, in an elongated organism, supply the force 

 for propulsion, the principle being that of the screw or propeller. An 

 additional forward component may be supplied by the flagellum itself if 

 it is swung backward as in Euglena viridis, but not if it is merely swung 

 outward more or less at a right angle as in Rhabdomonas incurvxim (334). 

 In such colonies as Volvox, the flagella are believed to act as propellers, 

 drawing water toward the points of attachment and thus creating for- 

 ward components of force. The stroke of the flagellum is so directed that 

 the Volvox colony usually rotates in swimming, although rapid swim- 

 ming without rotation also may occur (388). The ingenious experiments 

 of Brown (36) produced data which agree with the interpretations of 

 Lowndes, and indicate further that gyration of a flagellum alone also may 

 produce a fairly effective locomotor force. This possibility may explain 

 gliding in Peranema trichophorum, which Lowndes (333, 335) apparently 

 could not reconcile with his observations on other flagellates. 



Swimming in ciliates 



In two respects, rotation of the body on its long axis and the 

 usually spiral path of locomotion, swimming in ciliates resembles that 

 in various flagellates. Therefore, the principle of the screw or propeller 

 would seem applicable to swimming in ciliates also. However, the cilia 

 themselves apparently contribute a major forward component of force 

 in addition to causing rotation and gyration. This is indicated in the 

 "browsing" movements of ciliates along a surface during feeding. Move- 

 ment may be slower than in ordinary swimming, and particularly in 

 various hypotrichs, rotation of the body does not occur. The activity of 

 cilia, or their derivatives, is solely responsible for such movements. The 

 analysis of ciliary behavior in moving ciliates is a more difficult problem 

 than that of tracing flagellar movements. However, the activity of indi- 

 vidual cilia seems to be quite variable (36, 499), and may even include 

 spiral, flagellum-like undulations (36). Such a range of activity is presum- 

 ably correlated with the variety of maneuvers to be observed in ciliates. 

 The spiral path followed in swimming, as traced by Bullington (39) 

 in 164 species, shows a width, length, and direction rather characteristic 

 of each species. Both rotation and gyration are attributed to the com- 

 bined action of all the body cilia rather than a particular group. In 



