218 WALTER HE APE. 



showing the uneven surface of the zona, z., and its granular outer border. 

 The radial canals, r. c, passing through the zona, and the circum-vitelline 

 space between the vitellus and the zona, c. v. s. (Zeiss, imm. No. 2.) 



Fig. 7. — Small portion of the zona of the same ovum, more highly magni- 

 fied. The follicular epithelial cells,/. «., are here seen to be prolonged into 

 processes which enter the radial canals, r. c, passing through the zona. The 

 vitelline membrane, v. m., surrounding the ovum is here shown. (Zeiss, 

 imm. No. 3.) 



!FiG. 8. — Mature ovarian ovum. Vitellus has contracted, and a large 

 circum-vitelline space, c. v. s., left between vitelline membrane, v. m., and 

 zona, z. Vitellus has also contracted within the vitelline membrane, excepting 

 where amoeboid-like processes connect the two, and at a spot where a polar 

 body, ;;. b., is seen lying against but outside the vitelline membrane. A second 

 polar body lies freely in the circum-vitelline space. The female pronucleus, 

 /. P; is present within the ovum. (Zeiss d, occ. 2.) 



Pig. 9 — More highly magnified portion of the same ovum, showing two 

 polar bodies, p. b., outside, and female pronucleus, /. p., within the vitelline 

 membrane. 



Pig. 10. — Impregnated ovam. Male and female pronuclei, m . p. and / p., 

 are visible within the ovum. Two polar bodies and numerous spermatozoa, 

 sp., in the circum-vitelline space. (Zeiss B, occ. 2.) 



Fig. 11. — Ovum segmented into two. 



Fig. 12. — Ovum segmented into four. 



Fig. 13. — Ovum segmented into six. 



Fig. 14. — Ovum segmented into seven. 



Fig. 15. — Ovum segmented into eight. 



Fig. 16. — Ovum segmented into nine. 



Fig. 17. — Ovum segmented into fifteen. 



Figs. 18 and 19. — Ova segmented into a number of segments. 



The ova represented in Figs. 10 — 19 were all obtained from the Fallopian 

 tubes of moles. 



Fig. 20. — Fully segmented ovum obtained from the anterior end of the 

 uterus of a mole. The segments are now divided into an outer layer of 

 hyaline segments, o. I., and an inner mass of densely granular segments, i, m. 

 There is one spot on the circumference of the ovum where the hyaline seg- 

 ments are not continuous, and here one of the granular segments is inter- 

 posed. The layer of hyaline material m. c, outside the zona, is a coating of 

 mucous material which has collected there since the ovum entered the 

 uterus. 



Fig. 21. — Tlie ovum of a guinea-pig, segmented into four to show the large 

 yolk granules and the transparent appearance of the segments. 



