FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 25 



III. CROSS FERTILIZATION AND AGGLUTINATION IN Echinarach- 



nius AND Arbacia. 



We have seen in Part II. that the eggs of Echinarachnius in 

 sea-water liberate a substance comparable in every way to the 

 substance, fertilizin, liberated by Arbacia eggs. I have, there- 

 fore, used the term fertilizin for the Echinarachnius substance. 

 The problem that next presented itself was the study of cross- 

 fertilization in these two echinids whose sperm behave in the 

 same way to their egg secretions. In a relatively short time, a 

 rather curious, but as it turned out merely apparent, contra- 

 diction was in evidence: The cross was highly successful in one 

 direction only and the agglutination reaction ran counter to 

 and not parallel with cross fertilization capacity. This seemed 

 indeed worthy of study. A great deal of time, therefore, was 

 devoted to repeating the initial attempts at cross fertilization 

 and to determining the nature of, and the part played by, the 

 hetero-agglutinating substance. 1 



In this section I shall present first the results of the cross 

 fertilization and second some experiments which attempt to 

 analyze the significance of the hetero-agglutination. 



A. Reciprocal Cross Fertilization of Echinarachnius and Arbacia. 



With various methods many echinid crosses have been ob- 

 tained by a large number of workers; of these, the crosses by 

 Tennent and by Vernon may be particularly mentioned because 

 of the widely differing forms employed. The value of these 

 methods is discussed by Tennent and need not be commented on 

 here. Moreover, my object was not so much to test the relative 

 value of these methods for Arbacia-Echinarachnius crosses as to 

 test under the same conditions the response of the Arbacia egg 

 and of the Echinarachnius egg to foreign sperm. Comparison 

 of the capacity of the eggs for cross fertilization is made only 

 where the same method was employed on both eggs. And I may 

 say at once that while it is relatively easy to fertilize Echinarach- 

 nius eggs with Arbacia sperm, the reciprocal fertilization is 

 extremely difficult. 



1 Abundant material of both straight and cross fertilizations was fixed in a 

 number of fluids. The results of the study of this will appear later. 



