I08 THE AMERICAN ARBACIA 



fertilization membranes were not replaced. Refertilization could take 

 place even without removing the original fertilization membrane if 

 treated soon enough; and also in the 2-cell stage. 



p. Fertilization after Parthenogenesis 



Loeb thought this possible if the fertilization membrane was removed 

 from the parthenogenetic egg ( Strongylocentrotus purpuratus ) ; he thought 

 even blastomeres could be fertilized (Loeb, 19 13 a, p. 234, 237; 1914b; 

 1915 a, b). A reversal of parthenogenetic development and subsequent 

 fertilization could take place also in Arbacia eggs (Loeb, 1913 c; 

 Wasteneys, 1916). But others found that a subsequent fertilization 

 was not possible unless parthenogenetic treatment was incomplete 

 (C. R. Moore, 1916, 1917; F. R. LiUie, 1919, p. 167, 1921a; Just, 

 1922 a; Lillie and Just, 1924, p. 502). However, more recently Ishida 

 and Nakano (1947, 1950) have found that if the eggs of 5', pulcherrimus 

 were treated with a parthenogenetic agent (butyric acid) and the fert- 

 ilization membranes removed mechanically, and were then placed in 

 a Ca-Mg-free medium, they could be fertilized. Sperm entered and 

 cleavage took place similar to that characteristic of polyspermy. 



