cell-mass

—In the outer part of the intermediate cell-mass, immediately under the ectoderm, in the region from the fifth cervical to the third thoracic segments, a series of short evaginations from each segment grows dorsalward and extends caudalward, fusing successively from before backward to form the pronephric duct.

XI. Splanchnology. 3. The Urogenital Apparatus 1918

Development of the Urinary and Generative Organs—The urinary and generative organs are developed from the intermediate cell-mass which is situated between the primitive segments and the lateral plates of mesoderm.

XI. Splanchnology. 3. The Urogenital Apparatus 1918

The cells of the morula are at first closely aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which does not contribute to the formation of the embryo proper, and an inner cell-mass, from which the embryo is developed.

I. Embryology. 5. Segmentation of the Fertilized Ovum 1918

The primitive segments lie immediately under the ectoderm on the lateral aspect of the neural tube and notochord, and are connected to the lateral mesoderm by the intermediate cell-mass.

I. Embryology. 8. The Primitive Segments 1918

The mesoderm in the floor of the groove connects the paraxial with the lateral mesoderm and is known as the intermediate cell-mass; in it the genito-urinary organs are developed.

I. Embryology. 5. Segmentation of the Fertilized Ovum 1918

On the deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differentiated and quickly assumes the form of a small sac, the yolk-sac.

I. Embryology. 5. Segmentation of the Fertilized Ovum 1918

The inner cell-mass remains in contact, however, with the trophoblast at one pole of the ovum; this is named the embryonic pole, since it indicates the situation where the future embryo will be developed.

I. Embryology. 5. Segmentation of the Fertilized Ovum 1918

In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac (Figs. 24 and 32), and, as indicated on page 46, appears in the inner cell-mass as a cavity.

I. Embryology. 11. Development of the Fetal Membranes and Placenta 1918

The floor of this cavity is formed by the embryonic disk composed of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell-mass and lying in apposition with the entoderm.

I. Embryology. 5. Segmentation of the Fertilized Ovum 1918

Fluid collects between the trophoblast and the greater part of the inner cell-mass, and thus the morula is converted into a vesicle, the blastodermic vesicle (Fig. 10).

I. Embryology. 5. Segmentation of the Fertilized Ovum 1918