EGG-SECRETIONS OF ARBACIA AND ASTERIAS. 377 



opalescence due to the presence of the small amount of sperm in 

 B, or to the small traces of the purple "sperm-agglutinin" 

 compound which was necessarily formed in this tube. However 

 the relative densities of the colors in the three tubes did not 

 change, although the relative effect of the sperm as well as of the 

 purple compound could not have been as great at 10.10 as at 

 9.50, and 9.55. The same experiment was repeated several 

 times with more dilute suspensions of sperm, and very dense 

 suspensions of eggs. Exactly the same relative discolorations 

 were obtained. I mixed up the tubes on several occasions and 

 asked some one not familiar with the experiment to see if any 

 differences could be noted. I also had the tubes mixed and 

 handed to me for identification. In every case it took but a 

 moment to distinguish the tube in which fertilization had oc- 

 curred. This was true also in the absence of the tube containing 

 the double sea-water. 



One may say therefore that when equal quantities of unfertil- 

 ized Arbacia eggs are allowed to stand for equal lengths of time 

 in equal quantities of sterile and sperm-infected sea-water, the 

 discoloration of the supernatant liquid is greater in the case of 

 the eggs undergoing fertilization. This proves that something 

 in addition to water leaves the eggs at fertilization, a circumstance 

 not at all surprising in view of the fact that, whatever else it 

 may involve, fertilization is accompanied by an increase in 

 permeability. 1 The question whether there is in addition to the 

 quantitative difference, also a qualitative one, must for the 

 present remain open. 



1 Loeb ('i3 6 ) criticizes McClendon's evidence for increased permeability after 

 fertilization on the ground that more than one interpretation of the experimental 

 evidence is possible. My contention is not that the permeability of fertilized eggs 

 is greater than that of unfertilized, but that there is an increase in the permeability 

 of unfertilized eggs at the moment at which they are being fertilized. This idea 

 is expressed by R. S. Lillie, p. 290, " The Physiology of Cell Division," III. Direct 

 observational support for this view is furnished by F. R. Lillie's work on Nereis, 

 and more indirect evidence by my measurements of the rate of secretion by un- 

 fertilized eggs as compared with eggs undergoing the process of fertilization. The 

 decreased volume of the Arbacia and Asterias ovum after fertilization seems to me 

 unintelligible except as the result of an increase in permeability. Why it should 

 be assumed that this increase is more than momentary, I fail to see. 



