FERTILISATION OF THE EGGS OF ANIMALS. 159 



which WHS observed many times for both Arbacia and 

 Echinus, may be as follows : — The spermatozoa in the 

 zone c after using up all the oxygen at once come to rest. 

 The zones a and h are by diffusion supplied with oxygen 

 from the bubble of air. The spermatozoa in these zones are 

 thus able to continue in movement. This they do in any 

 direction until reaching the inner edge of the zone c ; when 

 the oxygen has all been used up they can move no longer, 

 and come to rest there, forming a ring. It is not, however, 

 clear to me why the zone h should not be as crowded 

 as the zone a. In any case there is no gathering of 

 motile spermatozoa in any zone around the air-bubble. The 

 phenomenon here described has then a totally different 

 appearance to that figured by Massart^ for the oxytaxis of 

 Spirillum and of Anophrys, and is also quite unlike the 

 collection of Spirillum und ula around air-bubbles, which 

 I myself have had frequent occasion to observe. I therefore 

 fail to see in the phenomenon any evidence that the sper- 

 matozoa are attracted by oxygen. 



From the above section of my paper it will be noticed that 

 I have been unable to obtain any evidence, either direct or 

 indirect, that the spermatozoa are attracted chemotactically 

 to the eggs, and that, further, no success has attended my 

 efforts to find any substance to which the spermatozoa are 

 chemotactically sensible. 



VI. The Movements op Spermatozoa upon Surfaces. 



When swimming in a drop of sea-water and not in contact 

 with its surface the spermatozoa of the Echinoidea swim 

 spirally. The spirals may be so steep that the spermatozoa 

 appear to swim in almost a straight line, and they tlien move 

 relatively rapidly across the field of the microscope. On the 

 other hand, the incline of the spiral may be so gentle that 

 the spermatozoa appear to be swimming almost in circles. In 



' Massarl, luc. cit., p. 157. 



