15. Viewed by means of a powerful microscope, the ovulum is found to consist of a small yellow spherical body, placed within the vesicula Graafiana, with the upper portion of which it is, internally, in contact; so that it does not float freely in the liquid of that vesicle. This contact becomes more and more intimate as the ovulum enlarges, when that part of the capsule of the vesicle which lies over it becomes, in a correspondent degree, thinner. 16. At first, the little yellow body, being rather opaque, is distinctly seen even without a magnifying glass; but as it advances, it becomes more transparent and, consequently, less distinguishable. 17. This little yellow body is a minute spherical mass, with a roughish or slightly granular surface, and is hollow. Its parietes are thick; around them is an envelope of a much thinner texture, which is distinctly seen, owing to a small space lying between it and the surface of the little yellow body, which space is filled with a fluid substance of a peculiar nature. 18. When FECUNDATION takes place, that part of the vesicle of Graaf to which adheres, internally, the ovulum, bursts, and the ovulum escapes with its external envelope, together with a small portion of the liquid peculiar to the Graafian vesicle, and thus it passes into the fallopian tube. 19. Independently of the external envelope, and within it, the microscope has detected, after fecundation, the existence of another covering, completely investing the little spherical yellow body. 20. The ovulum has been traced, after fecundation, into the cavity of the womb, where the external covering (17) becomes what Boer has called “the cortical membrane”, (_cortex ovi_ of the present work,) improperly considered as a uterine production by preceding writers, and denominated the _reflected_ caducous or deciduous membrane. 21. The more intimate covering of the yellow body of the ovulum, that which closely invests its surface, and appears only after fecundation, (19) is afterwards changed into what has been denominated the shaggy chorion: my observations and my plates shew this. Boer, however, professes not to know what becomes of it during the progressive intro-uterine development of the ovulum. 22. The hollow and spherical yellow body of the ovulum corresponds with the yelk or _vitellus_ of the ovum of oviparous animals, and from it all the other several parts of the fœtiferous ovum are derived or formed, as gestation advances, and a progressive development of the parts takes place, from within, without[1].