STUDY OF FERTILIZATION 435 



Agglutination by sodium phosphate is somewhat diilerent : 

 in this case agglutination is due to the formation at the cell- 

 surface of insoluble calcium phosphate. This agglutination 

 only occurs in the presence of calcium ions, and is reversed by 

 any substance which dissolves calcium phosphate, e. g. acids. 



The parallel drawn by Lillie between the phenomena of 

 agglutination of germ cells and those of bacterial cells is no 

 proof that the agglutinative properties of the germ cells is an 

 essential condition for fertilization. Both bacteria and germ 

 cells exhibit the phenomena of spontaneous agglutination. 

 The latter phenomenon has been described by the writer (8) for 

 the eggs of IStrongylocentrotus lividus, and the 

 physiological properties of the cells indicates clearly that the 

 same factors are involved as in experimental agglutination. 



Apart from such considerations it does not follow that because 

 the eggs give off a substance which causes spermatozoa to adhere 

 to one another, the same substance will cause a spermatozoon 

 to adhere to the egg. As pointed out elsewhere, a mere agglu- 

 tination of the egg and sperm is an inadequate picture of the 

 events which ultimately lead to the inclusion of the sperm into 

 the cytoplasm of the egg ; it is only when the cell-membranes 

 break down at the point of contact that an actual fusion can 

 occur much as a small drop of orthotoluidine is drawn into 

 a large drop of di-methyl-aniline (Darling, 4). 



According to the present view, therefore, the only essential 

 effect of egg-secretions upon the spermatozoa lies in the 

 capacity of these substances to increase the activity of the 

 sperm. In certain cases egg-secretions appear to have no effect 

 on spermatozoa and yet fertilization readily occurs ; this fact 

 is obviously explicable on the physical analysis outlined else- 

 where in this paper. 



Summary. 



1. The theory of artificial parthenogenesis put forward by 



Loeb meets with considerable difticulties when applied to the 



precipitates depends on the charge on the cell-surface, but the mechanical 

 effect of flocculation seems certainly due to these precipitates acting as 

 a common matrix for the cells. 



