THE PHYSIOLOGY OF FERTILIZATION 173 



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 invertebrates 

 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 in a series of experiments, hitherto unpublished, which 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 fertilization in the 

 starfish. 



The effect in the case of the sea urchin may be 

 shown by the following table: 



in Sea-Water 



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 fertili- 

 zations of eggs of Arbacia 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 



