SEXUAL ACTIVITY OF MALE RABBITS - 479 
normal, and they appear to be consecutive phases. 1. ‘Pro- 
gressive Vibratile’ motion consists of a rapid vibration of the 
after part of the flagellum propelling the sperm rapidly forward 
with the head moving practically in a straight line. The direc- 
tion, in the absence of currents, is random. This type of mo- 
tion would be well suited for a prolonged journey to the Fallopian 
tube. 2. ‘Undulatory tactile’ which normally follows type 1 is 
characterized by a slow lashing from side to side of the entire 
tail, causing the head and middle piece to sway back and forth 
through an are of sometimes 90 degrees. Only slight linear ad- 
vance is made in this phase and the path is exceedingly devious. 
Having arrived at the tube this kind of movement would provide 
that the sperm ‘find’ the egg. The sperm at this stage seem to 
be negatively thigmotactic, having the power to touch and back 
off from other bodies. 3. The third type succeeds the second 
and is distinguished by a ‘bunting’ action of the head and a 
rapid vibratile motion of the tail when in contact with another 
body. Reynolds considers that this type enables the sperma- 
tozoa to penetrate the egg membranes and to fertilize the ovum. 
The types of motion which are said to be abnormal will not be 
considered here. 
In our own work we have attempted to consider the type of 
motion present as well as the rate of motion, but we find it ex- 
ceedingly difficult to make definite statements in regard to this 
matter. Ina very general way our observations are in harmony 
with those of Reynolds, i.e., we find that the specimens of semen 
which show the largest amount of progressive vibratile move- 
ment as a rule show the longest duration of motion. But with 
the semen handled as herein described the essential cyclic nature 
of the different phases of motion as described by Reynolds is 
not clearly brought out; for example, even in the sperm of 
lowest ‘vitality’ as measured by duration of motion, ‘stationary 
bunting’ is the most usual type of motion. Further reference to 
type of motion will be made in the next section. 
