1. The flagellum is an active unit in so far that it generates at least a part of its own energy irrespective of the attached cell.
2. In all cases so far examined the impulses or waves start at the base of the flagellum and not at the tip.
3. As a wave passes along a flagellum there is always a certain amount of rotation of the tip of the flagellum.
4. A method for determining both the rate of swimming of the organism and the rate of beat of the flagellum is described.
5. The rate of transmission of an impulse along a flagellum has been measured. In Euglena viridis it was found to be of the order of 810 μ per sec. or well under a foot per minute, which is almost infinitely slow compared with the rate at which an impulse passes along a nerve.
6. The term “Tractellum” is discussed and its use should be discontinued. Tractella are simply ordinary flagella attached to the front end of the organism, the impulse starting at the base and not at the tip.
7. The rotation of the organism itself is due to the plane in which the flagellum beats. A high rate of beat of the flagellum does not necessarily imply a high rate of rotation of the organism.
8. The mechanics of the flagellum are discussed, but no attempt is made to discuss the nature of the movement within the flagellum though the slow rate of impulse is highly suggestive that it is a surface action comparable to heat conduction rather than radiation.
9. Flagella attached to the hinder end of the organism and pushing it through the water present certain mechanical difficulties and occur in nature rather seldom. The more stable mechanism is for either a single flagellum or a pair of flagella to be attached to the front end to push the organism through the water.