THE PHYSIOLOGY OF FER 1 ILIZATION 1 73 



is obvious that the examination of conditions that 

 impede or prevent fertilization without injury to the 

 life of the gametes must furnish means for analysis. 



It is a fact well known to embryologists that con- 

 tamination of the eggs of some marine invertcl^rates 

 with blood or tissue exudates of the species reduces 

 considerably the percentage of fertilization; it is there- 

 fore a common practice to wash the eggs once or several 

 times in sea-water before insemination. That this 

 effect is more or less specific was proved by the writer 

 in a series of experiments, hitherto unpublished, which 

 show that the filtered plasma of the coelomic fluid of 

 sea urchins which inhibits fertilization in sea urchins 

 actually increases the percentage of fertiHzation in the 

 starfish. 



The effect in the case of the sea urchin may be 

 shown by the following table: 



Percentage of _ 



Coelomic Plasma Percentage of 



in Sea-Water Eggs Segmented 



1 75 



5 10 



10 0.2 



20 0.2 



40 0.2 



100 o 



Control: same eggs in sea-water 75 



A series of dilutions of the filtered plasma was made 

 as shown in the left-hand column; and identical fcrtiU- 

 zations of eggs of Arhacia were made simultaneously in 

 each. An excess of sperm was used in each case. It 

 is clear that the plasma in this case had a strong inhib- 

 iting effect on the process of fertilization. 'The inhibi- 

 tion operates on the initial stages because membranes 



