160 A. H. REGINALD T.ULLER. 



this case the progress across the microscopic field is very 

 slow indeed. Between these extremes there is every grada- 

 tion. An approximation to the first case appears, however, 

 to be the rule with the most active spermatozoa. 



When a spermatozoon comes in contact with a glass surface 

 it is influenced by it in a curious manner. The spermatozoon 

 remains in contact with the surface, and, unless it becomes 

 immediately fixed to the glass, 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 focussed, 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 a 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 

 botii 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 clinging to surfaces and rotation upon them by the 

 spermatozoa in the manner explained is not limited to glass. 

 It takes place quite as well upon the surface of a drop 

 bounded by air, and it is easily seen upon the outer surface 

 of the gelatinous layer of eggs of Echinus which have 

 just been placed in sea-water. I have also sometimes 

 watched it (in the case of Echinus) upon the protoplasm 

 of the eggs and u[)on tlie vitelline membrane, whei'e it was 

 made possible by the looseness of the zona pellucida. The 

 nature of the surface for the phenomenon does not, there- 

 fore, appear to be of essential importance. 



The following rule was found to hold good: whenever the 

 spermatozoa of the Echinoidoa come in contact with a sur- 

 face they either become fixed to it at once or, more often, 

 they rotate upon it, and in the latter case, looking from them 

 to the surface in question, in a counter-clockwise direction. 



The phenomenon is most easily seen in open drops con- 

 taining not too many spermatozoa. The drops I employed 



