112 PROBLEMS OF FERTILIZATION 



whereas the sea urchin spermatozoa do not to the same 

 extent. The latter are, however, to be regarded as 

 always nearer the threshold of activity. Loeb points 

 out that the activating substance is different from the 

 agglutinating substance, because after removal of the 

 latter the activating substance is still found.' 



The relationship between activity of the spermatozoa 

 and presence of egg secretions may obviously be a sig- 

 nificant factor in fertilization, because it is probable that 

 completely immotile spermatozoa will not fertilize. 



b) Aggregation and agglutination. — If a drop of 

 Arbacia egg water be injected into a sperm suspension 

 of the same species beneath a raised cover slip a very 

 violent reaction may be observed under a low power 

 of the microscope. In the first second the spermatozoa 

 within the drop are aroused to intense activity and form 

 small agglutinated masses; these then fuse with the 

 greatest rapidity to form larger agglutination masses for 

 a period of three to five seconds, after which no more 

 fusion of masses takes place. While this has been 

 going on in the interior of the drop a ring has formed 

 at the margin, and a clear zone arises external to it. 

 The ring is at first continuous, but it ruptures in nu- 

 merous places in two or three seconds, and each segment 

 contracts quickly to an agglutinated mass. Such 

 masses, whatever their original form, quickly contract 

 into spheres. In a period of time varying from a few 

 seconds to a few minutes, depending on the concentration 

 of the egg water, the agglutination disappears. The 



^His statment that "Lillie seems to take it for granted that the 

 substance of the egg which causes sperm agglutination is identical with 

 the substance which stimulates the spermatozoa into greater activity" 

 rests upon no such statement of mine. 



