XX11 EXPLANATION OF PLATES. 



FIG. 



cells now occupying the greater part of the germinal vesicle b,- c, zona pellu- 

 cida: d, chorion, a new envelop, separated from the last by the fluid it has ab- 

 sorbed ( 746). 



14. 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 

 remains of the cells of which it is composed are seen at cho ( 747). 



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, b, which are undergoing a corresponding process of evolution into 

 secondary cells; c and d as in Fig. 13 ( 758). 



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



come to the surface, and showing the nucleus b 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 ( 758). 



17. Formation of the Membrana Decidua; a, a, a, villi of the mucous membrane^of the 



uterus; b, substance secreted between and upon these; c, uterine vessels pro- 

 longed into the decidua and forming loops. After Baer. 



18. Human Spermatozoa; a, seminal granules. After Wagner ( 735). 



19. Cyst of evolution. After Wagner ( 735). 



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



( 735). 



21. Globules fiom the Chyle; a, ordinary globules; b, a globule (cytoblastl) surrounding 



itself with an envelop (a forming cell?); c, minute molecules of chyle; d,a co- 

 lourless corpuscle from the blood. After Wagner ( 563). 



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



Barry ( 576). 



23. Extremity of one of the tufts of fetal vessels forming the Placenta ; this includes 



(like a branchial tuft) an artery and vein. After Reid ( 749). 



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



tion 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 foetal vessels, some of them sending down pro- 

 longed tufts which dip into the uterine sinuses ( 749). 



PLATE II. 



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



the embryonic cell (Fig. 14, 6) 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 Bischoff ( 760). 



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 

 ( 760). 



27. More advanced embryo, seen on its ventral side, and showing the first development 



of the Circulating apparatus. Around the Vascular Area is shown the terminal 



