A text-book of obstetrics / by J. Clarence Webster.

  • John Clarence Webster
Date:
1903
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of obstetrics / by J. Clarence Webster. Source: Wellcome Collection.

    23/810 page 21
    anywhere in its passage from the ovary to the uterine cavity. Some believe that the latter is the most frequent place of union, though most authorities think that it is probably the outer end of the Fallopian tube, as this appears to be a favorite resting-place of the spermatozoa. Nature of Fertthzation—This is unknown in the human female. It has been observed in several invertebrates—z. ¢., echinoderms, mollusca, ascarides, etc. Among the higher vertebrata various stages have been observed in different forms—z. ¢., dog, mouse, rabbit, etc. The spermatozoa penetrate the zona pellucida, though in what numbers is not known in the human subject. Kollmann has counted as many as sixty attempting penetration in the case of a bitch. In some of the lower animals there is an opening in the zona, known as the micropyle, through which the spermatozo6én FIG. 4.—Ovum of mouse, showing polar body (a) under the zona pellucida (c), and below it the rest of the nuclear spindle. At another point (0) there is an elevation near the surface, into which a spermatozoo6n (d@) has penetrated (Sobotta). enters. This is wanting in the human ovum. Though many may attempt an entrance, it is probable that only one performs the essential act of fertilization—z. ¢., blends with the female pro- nucleus. At the point where this one is about to enter, the proto- plasm of the ovum forms a swelling under the zona, known as the receptive prominence. Through this the spermatozoon bores its way, losing its tail, the head becoming the male pronucleus. Around it radial lines appear in the yolk protoplasm. The male and female pronuclei now move toward one another, and blending of the two occurs, followed by a short period in which they can- not be recognized. Soon they reappear as a single mass, hence- forth known as the segmentation or cleavage nucleus. Fertilization is now complete. Segmentation.—The early changes in the fertilized ovum have not been studied in the human subject, but they have been carefully investigated in several of the higher vertebrates and in
    digitised image 1
    digitised image 2
    digitised image 3