186 



Embryogenesis: Preparatory Phases 



Fig. 56. Macroscopic appearance of agglutination reaction in the keyhole limpet Megathura crenulata. 

 Photographed in Syracuse dishes, X Vi- a. Untreated sperm suspension (ca. 2 per cent); b, c, and d, 15 sec- 

 onds, 30 seconds and 10 minutes, respectively, after addition of solution of fertilizin. (After Tyler, '40a.) 



f^y li\ 



v^ 



c d 



Fig. 57. Photomicrographs of agglutinated sperm of the keyhole limpet Megathura crenulata. a. Three 

 agglutinates formed in a moderately strong solution of fertilizin, showing spherical shell of sperm heads sur- 

 rounding central mass of sperm; X 50. b. An agglutinate formed in a strong solution of fertilizin, showing 

 uicomplete shells of sperm heads attached to main mass by the ends of the tails; X 170. c and d, Fusion of 

 two agglutinates; d was photographed 15 seconds after c; X 85. (From Tyler, '40a.) 



