An introduction to the study of embryology / by Alfred C. Haddon.

  • Alfred Cort Haddon
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to the study of embryology / by Alfred C. Haddon. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

    78/374 page 44
    THE STUDY OF EMBRYOLOGY. of the blastopore of a Lizard. Mitsukuri and Isliikawa have very recently described a perfectly similar stage in the Turtle (Trionyx). Segmentation of the Mammalian Oosperm—Blastodermic Vesicle.—So far as is known, the oosperm of all the higher Mam- mals (Eiitheria) undergo total and, at first, regular segmentation. In the Kabbit, according to Van Beneden, the first furrow separates what he terms the epiblast from the hypoblast; but it will be better, for the present, to call them, with Heape, the outer and Fig. 39.—Sections through the Oosperm op THE Rabbit during thk Later Stages of Segmentation, showing the Formation of THE Blastodermic Vesicle. [Fro7n Quain, after Is. Van Beneden.] a. the outer-layer cells have entirely sur- rounded the inner-layer cells, except at one spot, the blastopore of Van Beneden; b. the enclo- sure is complete, and fluid is beginning to accu- mulate to foiTu the vesicle; c. and d. later stages ; ect. outer layer; ent. inner layer; zp. zona pellu- cida. inner layer cells (fig. 38). Each sphere divides into two, and these into two more spheres. In the eight-celled stage (fig. 38, c) one inner-layer cell is more centrally situated. Further segmentation results in a cap of smaller, more transparent outer-layer cells surrounding a solid mass of granular inner-layer cells (fig. 38, e). Eventually the latter are entirely surrounded, except at one spot, the so-called blasto- pore of Van Beneden (fig. 39, a), but this is also rapidly closed over. The outer layer next enlarges so as to form what is termed the
    digitised image 1
    digitised image 2
    digitised image 3