A. TYLER 



359 



in response to immunization with various materials of four spe- 

 cies of sea urchins. It may be noted that the fertihzin antisera are 

 consistently effective in this respect and that they are cross reac- 

 tive among three of the species used (S. purpuratus, L. picfus, 

 and S. franciscanus) , but possibly not with the fourth (A. punc- 

 tulata ) . In control sera, cleavage and development generally pro- 

 ceeded normally to swimming late blastula or early gastrula stage. 



Details of the results with the various antisera cannot be given 

 here. It may be noted, however, that the listing in Table I refers 

 to antisera that blocked cleavage effectively within the space of 

 one division after treatment. Some of the antisera gave retarda- 

 tion of cleavage and cessation of development at a late cleavage 

 stage. The majority of the nonblocking antisera permitted devel- 

 opment to proceed apace with the controls. 



The absorption with whole sperm, of blocking antisera pro- 

 duced against fertilizin or extracts of fertilized eggs, does not 

 remove the cleavage-blocking effect (Table II). However, an 

 antiserum against sperm extract (antifertilizin) that had retard- 

 ing action lost this property upon absorption with whole spenn. 



Table II. Absorption of Cleavage-Blocking Antisera 



