12 E. E. JUST. 



I. INTRODUCTION. 



The behavior of the sperm cells with reference to egg-extrac- 

 tives and the significance of this for the mechanism of fertilization 

 has been analyzed in detail only in Arbacia and in Nereis (Lillie, 

 '13, '14). It is true that the agglutination reaction had been 

 previously studied by various workers, but the role of this 

 phenomenon in fertilization as a specific reaction was not sug- 

 gested; and it is on this specificity that the fertilizin theory of 

 Lillie in large part rests; that is, that the egg alone secretes the 

 sperm-agglutinating substance and that this substance is neces- 

 sary for fertilization. It seemed desirable by study of this 

 agglutinating reaction to determine its role in fertilization in 

 some other form; this has been done in Echinarachnius parma. 

 The present paper is a contribution to the analysis of the role of 

 the sperm-agglutinating substance as revealed by a study of its 

 behavior in straight and in cross fertilization. The results 

 conform with those of Lillie, the data on cross fertilization seem- 

 ingly at variance actually giving support to the view that the 

 agglutination reaction is specific. The sperm agglutinin of 

 Echinarachnius is, therefore, identical in behavior with the 

 fertilizin of Arbacia. 



Although observations on Echinarachnius were made during 

 1914, and 1915, all experiments here reported except those cited 

 on page 22 are from those made, at the Marine Biological 

 Laboratory at Woods Hole, Mass., during the season of 1917, 

 beginning early in June. The experiments fall into two groups: 

 those on iso-agglutination and straight fertilization in Echi- 

 narachnius (Part II.) and those on hetero-agglutination and 

 cross fertilization with Arbacia (Part III.). 



II. SPERM AGGLUTINATION AND ITS SIGNIFICANCE IN 

 ECHINARACHNIUS. 



The mere fact that sperm are agglutinated by substances 

 dissolved in sea-water is of no special significance for us since 

 many substances will accomplish this; among others, alkalis, 

 polyvalent salts (Gray), and snake venom (Noguchi) ; but the 

 agglutinations by these agents are distinctly toxic and we must, 

 therefore, at the outset exclude them from consideration. They 



