TABLE OF CONTENTS. 



CHAPTER I. 



THE RIPE OVARIAN OVUM, pp. 213 221. 



Structure of ripe ovum. Atrophy of germinal vesicle. The extrusion of its 

 membrane and absorption of its contents. Oellacher's observations on the germinal 

 vesicle. Gotte's observations. Kleinenberg's observations. General conclusions 

 on the fate of the germinal vesicle. Germinal disc. 



CHAPTER II. 



THE SEGMENTATION, pp. 222 245. 



Appearance of impregnated germinal disc. Stage with two furrows. Stage 

 with twenty-one segments. Structure of the sides of the furrows. Later stages of 

 segmentation. Spindle-shaped nuclei. Their presence outside the blastoderm. 

 Knobbed nuclei. Division of nuclei. Conclusion of segmentation. Nuclei of the 

 yolk. Asymmetry of the segmented blastoderm. Comparison of Elasmobranch 

 segmentation with that of other meroblastic ova. Literature of Elasmobranch seg- 

 mentation. 



CHAPTER III. 



FORMATION OF THE LAYERS, pp. 246 285. 



Division of blastoderm into two layers. Formation of segmentation cavity. 

 Disappearance of cells from floor of segmentation cavity. Nuclei of yolk and of 

 blastoderm. Formation of embryonic rim. Appearance of a layer of cells on the 

 floor of the segmentation cavity. Formation of mesoblast. Formation of medullary 

 groove. Disappearance of segmentation cavity. Comparison of segmentation cavity 

 of Elasmobranchs with that of other types. Alimentary cavity. Formation of 

 mesoblast in two lateral plates. Protoplasmic network of yolk. Summary. Nature 

 of meroblastic ova. Comparison of Elasmobranch development with that of other 

 types. Its relation to the Gastrula. Haeckel's views on vertebrate Gastrula. Their 

 untenable nature. Comparison of primitive streak with blastopore. Literature. 



CHAPTER IV. 



GENERAL FEATURES OF THE ELASMOBRANCH EMBRYO AT SUCCESSIVE 



STAGES, pp. 286 297. 



Description of Stages A Q. Enclosure of yolk by blastoderm. Relation of the 

 anus of Rusconi to the blastopore. 



B. 14 



