_Motility_: After clinical observation of the motility of the spermatozoa of the bull, I find that it differs little or none from the types as observed by Reynolds (34) in his work on human spermatozoa. His observations are so accurate and well described that they will be given in his words. “All normal motions appear to be consecutive phases. Initial motion, i. e., motion as seen in fresh semen under favorable conditions, consists of a lashing of the after part of the tail from side to side which is so rapid as to constitute vibration. It produces rapid forward motion in a practically straight line, the head, middle piece, and forward portion of the tail maintaining their position in the line of motion with practically no swaying from side to side. The action of the flagellum is so rapid that it is quite impossible to follow its individual movements. Spermatozoa swimming in this manner head against the current and usually cross the field of observation in about five seconds in the absence of currents or obstacles. This type of motion will be described throughout the paper as ‘progressive vibratile’ motion. Progressive vibratile motion is normally succeeded after a variable length of time by what I regard as the second phase of normal motion. “The second normal motion differs from the first not only in its character but in markedly reduced speed. The tail movement alters to a long stroke from side to side and almost the whole length of the tail partakes in the stroke. This is, moreover, accompanied by swaying of the head and middle piece through an arc which is always considerable and may even equal ninety degrees. The general outline of the spermatozoa, from being practically straight with almost non-detectable sharp, quick, small arc vibration of the after-tail, has become an S in outline, with large, slow, plainly perceptible undulations traveling gradually backward throughout the length of the spermatozoon. Speed has been lost and direction seems to be more specifically determined by the surroundings. Individuals at this stage show a pronounced choice of direction and go up to objects in the medium, from which they later make off as though the movement were determined by tactile reaction to some extent. This type of motion has, therefore, been named ‘undulatory tactile’ in contradistinction to ‘progressive vibratile.’