CONTENTS XI 



h. Polyspermy 93 



i. Physiology 93 



j. Seminal fluid 93 



k. Techniques 93 



Chapter 13. Fertilization and Cleavage 95 



a. Fertilization 95 



b. Cleavage 96 



c. Schedule of development 97 



d. Cleavage without membranes 100 



e. Sperm entrance and cleavage planes 100 



f. The centriole loi 



g. Mid-bodies loi 



h. Chromosomes 102 



i. Visibility of the cleavage figure 103 



j. Isolation of mitotic apparatus 104 



k. Elongation at cleavage 104 



1. Asynchrony in cleavage 104 



m. Micromeres 105 



n. Absence of oxygen 107 



o. Refertilization 107 



p. Fertilization after parthenogenesis 108 



Chapter 14. Blastula, gastrula and pluteus 109 



a. Blastula and gastrula 109 



b. Pluteus, description 110 



c. Development when not fed 113 



d. Food for pluteus 113 



Chapter 15. Metamorphosis 115 



a. Arbacia punctulata 115 



b. Other species 117 



PART III. CENTRIFUGED EGGS 



Chapter 16. Methods 121 



a. Whole eggs 121 



b. Crushed eggs I22 



Chapter 17. Stratification of the egg granules 125 



a. Unfertilized eggs 125 



b. Vital staining of stratified egg 125 



c. Stained sections of stratified egg 125 



d. Stratification of other species 127 



