92 S. o. MAST 



tional in locomotion is shown by the fact that specimens with 

 the flagellum removed, an operation which was repeatedly per- 

 formed with a fine glass rod, are still capable of progressing, 

 although much more slowly than before the operation. The 

 activity of the flagellum is, however, alone sufficient to produce 

 locomotion, for specimens are frequently seen moving quite 

 actively and accurately in the direction of the flagellum when 

 the body is bent at right angles to it, so that contractions in 

 the body could not possibly function and still admit of move- 

 ment in the direction of the flagellum. When iodin is^ added 

 it not only induces marked contractions in the body but also 

 much more vigorous action of the flagellum. Not only do the 

 rate and the extent of vibration increase but a larger portion 

 becomes active. Under such conditions the portion of the 

 flagellum which vibrates increases from about one-sixth to 

 more than one-half, the angle in it being much nearer the body. 

 The combined effect of the increased activity in the flagellum 

 and the contractions in the body causes the rate of locomotion 

 to become almost double that ordinarily observed in crawl- 

 ing specimens. 



If the iodin solution is strong enough the crawling specimens 

 leave the substratum and swim freely through the water. I 

 have never seen this method of locomotion under ordinary 

 conditions; it must be very rare in nature. In swimming, the 

 entire flagellum is active, having a motion somewhat like that 

 of a snake except that it is not restricted to one plane but rotates 

 continuously on its long axis so that it appears much like a 

 cork-screw in motion. The body also rotates continuously 

 when the animal swims, usually counter clockwise, like most 

 of the free-swimming unicellular organisms, but the rotation 

 of the flagellum is independent of this; it may often be seen 

 when the body is stationary. As a matter of fact it is the rota- 

 tion of the flagellum that causes the rotation of the body. 



Reactions to Contact Stimuli. — The study of the reactions of 

 Peranema was confined almost entirely to crawling specimens. 

 As these animals move about they come in contact with objects, 

 the tip of the flagellum usually striking the object first. Often 

 when this happens there is no response. This is especially true 

 when the object is small or when it consists of a mass of loosely 

 compact granules or fibers, or when the flagellum strikes one 



