368 MARGARET FLOY WASHBURN 



case if the response to gravity is passive, are not mentioned 

 by Harper. 



Wager (32) made his observations upon plant forms, such as 

 Euglena viridis, Chlamydomonas, Volvox, and Spirillum, but 

 they apply equally to Protozoa. He was especially concerned 

 with the causes leading these organisms to form peculiar aggre- 

 gations and networks. These aggregations are not related to the 

 presence or absence of carbon dioxide ; they are due rather to 

 the forces of gravity and cohesion, "combined with the friction 

 of the water, which sets up a vertical motion as soon as the 

 Euglenae begin to fall." " During the aggregation there is a con- 

 stant cyclic movement downwards and upwards. The down- 

 ward movement is a passive one, the Euglenae being orientated 

 into a vertical position with their anterior end upwards." This 

 is because the posterior end is heavier; dead Euglenae sink in 

 the same position. The upward movement is active, but de- 

 pends upon this same orientation of the body. "The attraction 

 exerted by gravity is not effective unless the Euglenae are pre- 

 sent in large numbers. If they are few in number, they are 

 capable of moving in any direction, but always with a tendency 

 to move upwards. The aggregation into networks or groups 

 can only take place when the Euglenae are sufficiently crowded 

 together for the downward pull of gravity to be effective." 



The only study of the effect of light on the behavior of uni- 

 cellular organisms that has appeared during the year, that of 

 Desroche (6), is also concerned with plant life. The zoospores 

 of Clilamydomonas Stcinii Goros are found to maintain a con- 

 stant speed of movement unaffected by the light intensity. The 

 effect of light is not kinetic but orienting, the movements being 

 directed towards the light if it is sufficiently intense. 



McClcndon (17), Ulehla (31), and Mast (19) have made studies 

 of the motor processes in the Protozoa. McClendon attempts to 

 show the relation of protoplasmic movement to the forces in a 

 magnetic field. Ulehla, by means of the paraboloid condenser, 

 has made a minute analysis of the movements of the flagellum 

 in various species of flagellates. He finds that these movements 

 are seldom those of simple rotation ; various figures are described 

 which are peculiar to the species. The flagella have a very com- 

 plex internal structure, and a very rapid rate of movement. 

 The regularity of their beat is not easilv disturbed. Their action 



