EXPLANATION OF PLATES. 



PLATE I. 



The first 16 Figures in this Plate are from Dr. Barry's Embryological Researches in the 

 Philosophical Transactions for 1837, 1839 and 1840. 



FIG. 



1. A very early stage of the formation of the Ovum ; the vesicles, the largest of which 



measures only 1-1 125th of an inch, are seen in the midst of dark granules or 

 globules ( 740). 



2. A stage somewhat more advanced; the vesicles are surrounded by envelops of 



smaller vesicles, amongst which the granules are still seen ( 740). 



3. A still later stage ; a central vesicle, a, is seen, with a spot, b, upon its walls, and 



surrounded with numerous granules; this has now evidently become the Germi- 

 nal Vesicle ( 740). 



4. Ovisacs from Human Ovum, l-200th of an inch, and upwards, in diameter; the 



largest exhibits the Germinal Vesicle, a, very distinctly ( 740). 



5. Ovisac from Cat, showing its contents when near matarity; a, ovisac; b, its con- 



tained granules ; c, zona pellucida; d, granules of the yolk; e, germinal. vesicle ; 

 /, germinal spot; magnified 440 diameters ( 739). 



6. Ovum of Rabbit at the periphery of the Graafian follicle, with part of the membrana 



granulosa removed; g, g, membrana granulosa; ov, ovulum; r, retinacula ( 

 740, 744). 



7. Ovum with its tunica granulosa and retinacula, removed from the Graafian follicle; 



a, germinal vesicle; b, germinal spot; c, zona pellucida; d, globules of the yolk; 

 r, r, retinacula ; t g, tunica granulosa ( 740). 



8. Graafian follicle discharging its Ovum, ov, to which the tunica granulosa, t g, and re- 



tinacula, r, r, remain attached ( 744). 



9. Ovarium Ovum in preparation for fecundation ; a, germinal spot, beginning to resolve 



itself into cells at its margin ; b, germinal vesicle ; c, elliptical cells in the place 

 of the yolk; d, zona pellucida. 100 Diameters ( 745). 



10. Ovum nearly ready for fecundation: a, germinal spot more fully developed into cells, 



of which concentric layers occupy the germinal vesicle bf c, elliptical discs or 

 cells; d, zona pellucida; e, outer layer of cells of yolk ( 745). 



11. Fecundated Ovum of nine hours; the germinal vesicle, having returned to the centre 



of the ovum, is concealed by the large elliptical discs, which fill the cavity of 

 the zona pellucida ( 745, 746). 



12. Plan of one of these discs or cells: its nucleus, , has developed itself into con- 



centric rings of cells : and in the most fully developed of these, the nucleus, b, 

 is seen to be commencing the same kind of evolution. In the centre of the 

 original nucleus, a pellucid spot, the nucleolus of Schwann and Schleiden, is 

 observed ( 745). 



13. Ovum from the Uterus, measuring about l-68th of an iocb in diameter: a, pair of 



