LIST OF ILLUSTRATIONS. 



FIG. PAGE 



1. Human Spermatozoa, {afler Retzius), 44 



2. Full-grown Human Ovum before Maturation, [after W. Nagil), 46 



3. Ovum of a Worm (Sagitta) with Two Pro-nuclei. Around Each Pro-nucleus is shown the Aster 



{after O. Hertivis;), 52 



4. Ovum of a Rabbit, Seventeen Hours after Coitus, with the Pro-nuclei about to Conjugate {after Rein), 52 



5. Ovum of White Mouse. Beginning of the Conjugation of the Pro-nuclei (rty?^r 6'<?^(7//rt), 53 



6. Ovum of White Mouse. Conjugation of the Pro-nuclei, and Formation of the Segmentation Spindle 



[after Sobotta), c? 



7. Ovum of White Mouse. First Segmentation Spindle with the Chromosomes of the Pro-nuclei still 



forming Two Distinct Groups [after Sobotta), 53 



8. Ovum of a Rabbit' of Twenty-four Hours [after Caste), 55 



9. Ovum of a Snail (Limax campestris) during the First Cleavage. The Envelopes of the Ovum are 



not Drawn in [after E. L. Mark), 55 



10. Ovum of White Mouse. First Segmentation Spindle with Equatorial Plate of Chromosomes [after 



Sobotta), e6 



11. Ovum of White Mouse. First Segmentation Spindle (rty?!?;- 5'i)3o//f?), 56 



12. Ova of White Mouse with Two Segmentation Spheres or Cells (fl//f;- 5'(7^(7//«), 57 



13. Ovum of a Bat ( Vesperlilio murina) with Four Segmentation Spheres [after van Beneden and Julin), 58 



14. Ovum of a Virginian Opossum, with Four Segments (<7/?fr ^>/?7 ^■f/fw/ja), 58 



15. Rabbit's Ovum of about Seventy Hours [after E. van Beneden), 59 



16. Young Blastodermic Vesicle of a Mole [after W. heafe), 59 



17. Sections through the Inner Mass of Blastodermic Vesicles of the Mole at Three Successive Stages 



[after W. Heape), 61 



18. Transverse Section through the Embryonic Shield of the Blastodermic Vesicle of a Dog of Eleven 



or P'ifteen Days (Precise Age Unknown) [afler Bonnet), 62 



19. Surface View of the Embryonic Shield of the Blastodermic Vesicle of a Dog of Thirteen to Fifteen 



Days (Precise Age Unknown) [afler Bonnet), 63 



20. Central Portion of a Sheep's Blastodermic Vesicle of Twelve to Thirteen Days [after Bonnet), . . 64 



21. Blastodermic Vesicle of a Rabbit of Seven Days. Portion of the Mescderm of the Area opaca 



[after Kolliker), 64 



22. Germinal Area of a Guinea-pig at Thirteen Days and Twenty Hours, seen from the Under (Ento- 



dermal) Side, 66 



23. Transverse Section of a Mole Embryo (Heape's Stage H) [after W. Heape), 67 



24. Degenerating Tissue of the Notochord from the Central Portion of the Intervertebral Disc of a Cow's 



Embryo [after Leboucq), 69 



25. Surface View of the Embryonic Shield of a Dog Embryo, with Medullary Plate, 69 



26. Cross-section of a Human Embryo of 1.54 mm. [after Count Spee), 70 



27. Section of a Young Cat Embryo and of the Uterine Wall to Which it is Attached. (Embryo No. 



398, Section 76), 72 



28. Transverse Section of a Rabbit Embryo of Eight Days and Two Hours, 73 



29. Three Diagrams of Embryonic Areas of Chicks to show the Growth of the Mesoderm [after Duvai), 75 



30. Transverse Section of an Early Stage of an Axolotl [after Bellonci), 77 



31. Generalized Diagram of an Amniote Vertebrate Embryo, 78 



32. Transverse Section from a Chick Embryo with about Eighteen Segments, 80 



33. Section of a Very Young Cat Embryo. (Transverse Series 413, section 181), 81 



34. Diagrammatic Section of the Yolk of a Hen's Egg at an Early Stage to show the Relation of the 



Primitive Entodermal Cavity, 85 



35. Wall of the Yolk-sac in the Region of the Area opaca of a Chick of the Second Day 86 



