172 THE PHYSIOLOGY OF REPRODUCTION 



and partly upon the lower surface of the cover-glass. In these 

 positions they describe circles with their tails, the rotation being 

 invariably counter-clockwise. The bulk of the liquid remains free 

 from spermatozoa, the latter adhering to the glass surfaces after 

 having once reached them. If a ball be placed in the fluid, its 

 surface is soon sought by the spermatozoa. 1 Verworn has described 

 this phenomenon under the name of " barotaxis," and states that it 

 is caused by pressure acting unequally on different sides of the 

 spermatozoon. It is said to be of great importance in the process of 

 fertilisation, and probably assists the spermatozoon in entering the 

 micropyle of the ovum. 2 Dewitz's observations were subsequently 

 confirmed by Ballowitz. 3 



Counter-clockwise rotation upon surfaces was first recorded for 

 the spermatozoa of Echinoderms by Dungern, 4 who discovered the 

 phenomenon in SphasredwMts and Arbacia-. About the same time 

 Buller, 5 who has described the manner of rotation more fully, 

 observed its occurrence in the sperms of various other Echinoderms ) 

 and particularly in those of Echinus : " When a spermatozoon comes 

 in contact with a glass surface, unless it becomes immediately fixed 

 to the glass [it] begins to make characteristic circular revolutions 

 upon it. If the cover-glass be supported by pieces of another cover- 

 glass, and the upper surface of the drop in contact with it be carefully 

 focused, it is seen that all the spermatozoa which are not attached 

 by their heads, but are moving there, are revolving from the 

 observer's point of view in clockwise direction. If the lower surface 

 of the drop in contact with the slide be examined, a reverse rotation 

 the counter-clockwise is seen to be the rule. In both cases, 

 therefore, if the surfaces be regarded from the point of view of the 

 spermatozoa, the rotation is always in one direction namely, the 

 counter-clockwise." 



The head is the only visible part of the rotating spermatozoon. 

 This moves rapidly round in a circle, which in the case of Ediiiw* is 

 slightly less than 0'05 millimetre (or the length of a spermatozoon) 

 in diameter. A normally rotating sperm of Sj'/m /vr// ?'//* was 

 observed to make 100 circles around one point in ninety seconds. 

 The rate of movement of the head is calculated to be about 012 

 millimetre per second, or 7'2 millimetres per minute. 



The characteristic rotation may likewise take place upon surfaces 



1 Ballowitz, " Untersuchungen iiber die Struktur der Speruiatozoen, etc.," 

 /-./. A*,!., vol. i., 1890. 



- V.i won), tl.i.-ral Physiology, Lee's Translation from the second German 

 Kdition, Indon, 1899. 



3 Ballowk/, fi><: , ,t. 



4 Dnngern, "Die I'rsachen der Specietat bei der Befruchtung," Zentralbl. f. 

 ri. : i*iol., vol. xv., 1901. 



* Buller, foe. 



