LIST OF ILLUSTRATIONS 



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FIG. i. SPERMATOZOA OF VARIOUS ANIMALS .... 49 



FIG. 2. DRAWINGS FROM PHOTOGRAPHS OF Nereis EGGS 



IN A SUSPENSION OF INDIA INK IN SEA-WATER 52 



FIG. 3. PENETRATION OF THE SPERMATOZOON IN THE EGG 



OF Nereis, FROM SECTIONS 54 



FIG. 4. SPERMATOZOON IN THE OLIGOCHAETE Rhynchelmis, 

 IN THE EGG OF THE BAT Vespertilio voctula, 



AND IN THE EGG OF THE SNAIL PhySd 



fontinalis 56 



FIG. 5. THE FORMATION OF THE FERTILIZATION MEM- 

 BRANE IN THE EGG OF THE SEA URCHIN 



Strongylozenlrotus purpuratus 58 



FIG. 6. ENTRANCE OF SPERMATOZOON AND FORMATION 

 OF THE FERTILIZATION MEMBRANE IN Ascaris 

 megalocephala 59 



FIG. 7. FERTILIZATION OF THE EGG OF THE SEA URCHIN 



Toxopneustes 61 



FIG. 8. SECTIONS OF SUCCESSIVE STAGES SHOWING THE 

 INTERNAL PHENOMENA OF FERTILIZATION IN 

 Nereis 62-63 



FIG. 9. DEVELOPMENT OF Ascaris megalocephala, AND 



Pterotrachea AT VARIOUS STAGES .... 66 



FIG. 10. FERTILIZATION OF A NEMATODE (Ancyracan- 



Ihus cystidicola) 69 



FIG. ii. EFFECTS OF CENTRIFUGAL FORCE ON PENETRA- 

 TION OF THE SPERMATOZOON IN Nereis . . 72 



FIG. 12. HORIZONTAL SECTION OF THE GERMINAL DISK 



OF THE PIGEON'S EGG . .... 79 



FIG. 13. PHOTOGRAPH OF THE AGGREGATION OF A SPERM 



SUSPENSION 6r Nereis 95 



XI 



