20 



as to constitute vibration. It produces rapid forward motion in a 

 practically straight line, the head, middle piece, and forward por- 

 tion 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 indi- 

 vidual 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 'pro- 

 gi'essive vibratile' motion. Progressive vibratile motion is nor- 

 mally 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, accom- 

 panied 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 vibra- 

 tion of the aftertail, 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 

 inbratile. ' 



'The third type of normal motion succeeds the second and con- 

 sist.s in a tendency on the part of the spermatozoon to push itself 

 against or into any small masses of cells, or sometimes other 

 materials, which it may find in the neighl^orhood, bunting itself 

 into any small cove that can be found, and maintaining a slight 

 burrowing motion by a lashing tail movement of the vibratile type 

 not unlike the movements of the caudal fin of a fish. The move- 

 ment of the flagellum in this third type is unlike the second type 

 in that it is wlbratile rather than lashing, but is slower than the 

 \nbratile motion of the first type and less limited to the after- 

 part of the tail. The?e spermatozoa are apparently not caught 

 in the debris or unable to move off. From time to time, they 

 back out of such a cove and seek another mooring place. 



"This 'stationary bunting' motion is less universal than the 

 other two. Many individual spermatozoa fail to attain it. It 

 seems probable that only the most vigorous individuals ever reach 

 this stage. It has not been encountered in unmixed semen or in 

 any artificial mediums. It has been observed only when the sper- 

 matozoon is in the secretions of the female genital tract. It is 



