SPERM-EGG INTERACTING SUBSTANCES, I 27 



such as Arbacia punctulata, agglutinates the spermatozoa of a 

 distantly related organism, such as Nereis succinea, the same re- 

 action is elicited by blood, body fluids and sperm extracts; but 

 when the organisms under examination are closely related, these 

 latter substances do not agglutinate spermatozoa. A serum or body 

 fluid may contain a large number of independently absorbable 

 agglutinins, each of which exhibits group specificity, in the sense 

 of reacting with particular spermatozoa. In the serum of Panulirus 

 interruptus (Randall), for example, there are ten serologically dis- 

 tinguishable agglutinins, eight of which react specifically with the 

 blood or spermatozoa of scyphozoans, phanerocephalid polychaets, 

 holothurians, asteroids, ascidians, amphibians, reptiles and birds, 

 but not with the blood or spermatozoa of, for example, anthozoans, 

 cryptocephalid polychaets or turbellarians (Tyler & Metz, 1945). 

 These hetero-agglutinins are all present in a protein fraction which 

 is homogeneous on the basis of electrophoresis and ultracentrifuge 

 measurements. In the same way, parts of the fertilizin molecule 

 may carry such hetero-agglutinating properties. F. R. Lillie also 

 based his view that the hetero-agglutinating power of egg water 

 was due to the presence in it of a substance distinct from iso- 

 agglutinin on the observation that the hetero-agglutinin in the 

 egg water of Arbacia punctulata could be removed by sperma- 

 tozoa of Nereis succinea, though after the removal, the egg water 

 would still iso-agglutinate Arbacia spermatozoa. According to 

 Tyler (1948), the correct interpretation of this experiment is that 

 the fertilizin molecule has both hetero- and iso-agglutinating pro- 

 perties and that the inactivation of some molecules in a solution 

 through a hetero-agglutination reaction would not make much 

 difference to the iso-agglutination titre of the solution. A similar 

 situation exists in human blood sera which contain hetero- 

 agglutinins for the red blood cells of other vertebrates, though they 

 may not be distinct from the iso-agglutinins which distinguish the 

 blood groups. 



To sum up this section, the reactions of fertilizin are dominantly 

 species specific ; cross reactions occur mainly with spermatozoa of 

 closely related organisms. The occasional cross reactions with 

 spermatozoa of remotely related organisms are due to the similari- 

 ties between certain molecular configurations in the fertilizin 

 molecule and those in other proteins in the body fluids or blood of 

 the organism in question. 



