STUDIES OF FERTILIZATION 571 



is obvious that the size of the tube is a fundamental condition of 

 the experiment, both because the diffusion is a factor of size 

 and also because of the interference of thigmotactic reactions of 

 the spermatozoa at the mouth of the tube with the purely chemo- 

 tactic response. Duller does not state what was the size of the 

 tubes that he used in his experiments. But, if the delicacy of the 

 reaction was reduced to one-twentieth by the tube, his failure to 

 get a positive reaction in tubes containing sea-water taken from 

 over eggs is not surprizing. 



Von Dungern drew his conclusions from observing the behavior 

 of spermatozoa mixed with eggs. Many embryologists, like 

 myself, have made hundreds of observations of this kind ; but it 

 is obvious that the conditions thus created render an analysis of 

 the behavior of the spermatozoa impossible. In some experi- 

 ments I introduced a drop of eggs in sea-water into a sperm 

 suspension beneath a raised cover, and obtained the typical ring 

 formation of spermatozoa with reference to the group of eggs 

 considered as a whole. But within the group any evidence 

 of chemotactic reaction is clearly impossible. 



As to the role that chemotaxis as a principle may play in the 

 fertilization of the ova in nature it is difficult to form a clear con- 

 ception. It may be little and it may be considerable. In the 

 first place it may be noted that, although the echinids have been 

 favorite subjects for research, but little appears to be actually 

 known concerning their breeding behavior. In the second place 

 we do not know the distance to which the secretion from an iso- 

 lated egg will diffuse. But even if we assume that it extends 

 effectively only a short distance in terms of the egg-diameter the 

 result would be essentially to immensely increase the chances of 

 scattered spermatozoa to become entangled in the jelly of the 

 egg. iVIeasurements of the effective radius of diffusion of the 

 egg-secretion could, I believe, readily be made by the method 

 employed in my work and the results of this might enable us to 

 form some clearer idea of the possible significance of chemo- 

 taxis taken by itself in the meeting of the germ-cells. 



The present results merely show that it may be a factor of some 

 significance. The quickness and readiness of the reaction of 



