THE DEVELOPMENT OF THE MOLE. 217 



19. E. A. ScHirER. — " On the Structure of the Immature Ovarian Ovum in 



the Fowl and Rabbit," &c., ' Proceedings of the Royal Society,' xxx, 

 1880. 



20. Karl Sohulin.— " Zur Morphologie des Ovariums," ' Archiv fiir Mikros- 



kopische Anatomie,' xix, 1881. 



21. D. VON Sehlen. — " Beitrage zur Frage nach d. Mikropyle d. Saugethiere," 



'Archiv fiir Anatomie und Physiologie,' pt. i, 1882. 



22. H. ViacHOW. — " Durchtreten von Granulozen-Zellen durch die Zona- 



pellucida des Saugethiereies," ' Archiv fiir Mikroskopische Anatomie,' 

 xxiv, 1884. 



EXPLANATION OP PLATE XXI, 



Illustrating Mr. W. Heape's Paper on " The Development of 

 the Mole (Talpa Europea), the Ovarian Ovum, and 

 Segmentation of the Ovum." 



Reference Letters. 

 c. V. s. Circnm-vitelline space. /. e. Follicular epithelium. / p. Female 

 pronucleus, g. Granules within nucleus, m. e. Mucous coat. m. p. Male 

 pronucleus, n. Nucleus, nc. Nucleolus, p. b. Polar body. r. c. Radial 

 canals, sp. Spermatozoa. v. m. Vitelline membrane, y. lolk. z. Zona 

 radiata. 



All the figures are drawings of the ova of the mole, except Fig. 21, which 

 represents a guinea-pig's ovum. Figs. 13 — 19 have been copied for me by Mr. 

 H. A. Chapman. 



Fig. 1. — Ovarian ovum not yet ripe, surrounded by follicular epithelial 

 cells,/, e. The outline of these cells is to be seen through the transparent 

 zona, z. The outer edge of the zona is granular. A vitelline membrane may 

 be distinguished here and there. (Zeiss d, occ. 3.) 



Fig. 2. — A ripe ovarian (JVum. A few follicular epithelial cells only remain 

 attached to the zona. Network of protoplasm permeating the vitellus 

 (Zeiss D, occ. 2.) 



Figs. 3, 4, and 5. — Nuclei of three mature ovarian ova, similar to that 

 drawn in Fig. 2. Single nucleolus, nc, and large and small granules, g., in 

 each nucleus. Yolk vesicles, y., and granules surrounding nucleus in Fig. 4. 

 (Zeiss r, occ. 2.) 



Fig. 6. — A portion of the circumference of ovum represented in Fig. 2, 



16 



