l6 E. E. JUST. 



When species sperm comes in contact with an egg, it gains 

 entrance and fertilizes against the blood present. The greater the 

 amount of blood, the more difficult the fertilization. Indeed, the 

 blood may actually inhibit fertilization in every egg. Therefore, 

 dense sperm suspensions must be employed for fertilization in the 

 presence of blood rich in inhibitor. The blood inhibitor acts by ( 

 binding the fertilizin so that the fertilizin can not react with the 

 egg receptors. Heavy insemination insures fertilization perhaps 

 by increasing the chances of some spermatozoa locating fertilizin 

 free of blood inhibitor. Or in heavy insemination the onslaught 

 of numerous sperm brings it about that the fertilizin shakes free 

 the inhibitor. 



The blood slowly leaves the egg as it lies in sea-water. But 

 the fertilizin also goes. Hence while the egg is losing inhibitor 

 it is also losing fertilizing power. The blood is perhaps never an 

 irremovable block to species sperm; however, though present in 

 but a trace, it serves to block foreign sperm. In staling, therefore, 

 what results is not only loss of fertilizin, but also loss of blood. 

 The loss of blood makes possible cross fertilization. 



What is true of staling is doubtless true of other methods for 

 obtaining cross fertilization — heat, use of alkali, and of dilute sea- 

 water; they serve to remove the blood block. The fertilizin re- 

 mains albeit in reduced quantity. Whenever an egg is capable of 

 fertilization it possesses the fertilizable substance. And it is safe 

 to assume that an egg that will not respond to its own sperm will 

 not cross fertilize. 



From this point of view, then, fertilizin is not the only factor 

 in specificity. It is specific since it engages species sperm against 

 the inhibition of blood. But the blood is an aid to specificity, since 

 it blocks all sperm, species sperm least of all. 



LITERATURE. 

 Just, E. E. 



'19 The Fertilization Reaction in Echinarachnius parma. II. The Role of 

 Fertilizin in Straight and Cross Fertilization. Biol. Bull., XXXVI., 

 11-38. 

 Lillie, F. R. 



'14 Studies of Fertilization. VI. The Mechanism of Fertilization in Ar- 



bacia. Jour. Exp. Zo'dl., XVI., 523-590. 

 '19 Problems of Fertilization. The University of Chicago Press. 



