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 l-1125th of an inch, are seen in the midst of dark granules or 

 globules ( 906). 



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



vesicles, amongst which the granules are still seen ( 906). 



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



rounded with numerous granules ; this has now evidently become the Germinal 

 Vesicle ( 906). 



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



exhibits the Germinal Vesicle, a, very distinctly ( 906). 



5. Ovisac from Cat, showing its contents when near maturity; a, ovisac; b, its contained 



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

 spot; magnified 440 diameters ( 905). 



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 ( 906, 

 912). 



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 ( 906). 



8. Graafian follicle discharging its Ovum, ov, to which the tunica granulosa, tg, and retina- 



cula, r, r, remain attached ( 912). 



9. Ovarium Ovum in preparation for fecundation : a, germinal spot beginning to resolve it- 



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

 the yolk; d, zona pellucida. 100 Diameters ( 915, 916.) 



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



which concentric layers occupy the germinal vesicle b ; c, elliptical discs or cells ; 

 ?, zona pellucida; e, outer layer of cells of yolk ( 130, 915, 916). 



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 ( 916). 



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



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 ( 130, 916). 



