XX EXPLANATION OF PLATES. 



TIG. 



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

 now occupying the greater part of the germinal vesicle b ; c, zona pellucida ; d, 

 chorion, a new envelope, separated from the last by the fluid it has absorbed 

 ( 130, 917). 



34. Ovum, of which the essential part, a, the pair of cells occupying the germinal vesicle, 

 has advanced further than in the last case; the other contents of the germinal 

 vesicle have undergone liquefaction. The chorion is here incipient; and the re- 

 mains of the cells of which it is composed are seen at cho ( 130, 918). 



15. More advanced ovum; the cavity of the germinal vesicle filled with cells, a, that have 



originated in the two represented in the last figure; these cells have nuclei, 6, 

 which are undergoing a corresponding process of evolution into secondary cells ; c 

 and d as in Fig. 13 ( 130, 935). 



16. Ovum in a state rather more advanced; a, central cell of the germinal mass, now come 



to the surface, and showing the nucleus 6 with a pellucid centre, from which most 

 of the embryonic structures are developed ; c, cavity in the germinal mass, caused 

 by the approach of its peripheral cells to the enclosing membrane, d ( 935, 936). 

 17: Formation of the Membrana Decidua; a, a, a, interfollicular substance of the mucous 

 membrane of the uterus ; 6, cavities of the follicles ; c, uterine vessels prolonged 

 into the decidua and forming loops. After Baer ( 919). 



18. Human Spermatozoa; a, seminal granules. After Wagner ( 902). 



19. Cyst of evolution. After Wagner ( 902). 



20. Capsular bundle of Spermatozoa, just previous to their separation. After Wagner 



( 902). 



21. Globules from the Chyle; a, ordinary globules; b, a globule (cytoblast ?) surrounding 



itself with an envelope (a forming cell?); c. minute molecules of chyle; d, a 

 colourless corpuscle from the blood. After Wagner ( 692, 693). 



22. Particles of Blood undergoing multiplication : a, b, c, d, e, successive stages. After Barry 



( 148). 



23. Extremity of one of the tufts of foetal vessels forming the Placenta; this includes (like 



a branchial tuft) an artery and vein. After Reid ( 922). 



24. Plan of the structure of the Placenta, according to Dr. J. Reid's view of it ; a, a, portion 



of substance of uterus ; b, b, b, b, section of uterine sinuses, some of them opening 

 on the inner surface into the cavity of the placenta; c, curling artery of uterus ; d, d, 

 ramifications of fcetal vessels, some of them sending down prolonged tufts which 

 dip into the uterine sinuses ( 923). 



PLATE II. 



25. Uterine Ovum of Rabbit, showing the Area Pellucida, with the annular nucleus of the 



embryonic cell (Fig. 14, b) now elongated. In the clear space enclosed by this is a 

 well-marked dark groove, occupying the position in which the nervous centres are 

 subsequently to be developed. The cephalic extremity of this is already rounded 

 and the caudal extremity pointed. After BischofT ( 937). 



26. More advanced ovum, showing the incipient formation of the Vertebral column ; and 



the dilatation of the primitive groove at its anterior extremity. After Bischoff 

 ( 937). 



