Studies on the eel sperm flagellum. 3. Vibratile motility and rotatory bending.

A further account is given of motility in this 9 + 0 flagellum, where the axoneme is of special interest because it is powered by only inner dynein arms. Under some circumstances, normal motility is inactivated and yet the flagellum swims (or appears to glide) forward, albeit much more slowly. The propulsive thrust in these cases is due to a vibratile motion of the flagellum. Vibratile motion has a very small amplitude and is very rapid, but a frequency could not be determined stroboscopically. Provided that the sperm head is in place, a vibratile sperm can be stimulated mechanically such that it instantly resumes and continues normal motility. This indicates that a suprathreshold deformation of the axoneme triggers normal motility and that the threshold is normally continuously exceeded by a self-generated fluid-mechanical interaction in which the sperm head plays a necessary part. Without a sperm head, the flagellum propels itself by vibratile motion. Some vibratile sperm, found to be stuck by their heads, perform also a slow rotatory (clockwise) bending at the base of the flagellum. When this happens, there is no rotation of the axonemal substance. Therefore, this is interpreted as sequential, clockwise, self-perpetuating, circumferential activity around the arrays of inner dynein arms. The phenomenon is considered to be a restricted representation of the rapid clockwise (i.e., sinistral) helical wave of normal motility.