Henry Gray (1825–1861). Anatomy of the Human Body. 1918.
pages 1209
| organ; it soon loses its connection with the central mass, and a tunica albuginea develops between them. The ova are chiefly derived from the cells of the central mass; these are separated from one another by the growth of connective tissue in an irregular manner; each ovum assumes a covering of connective tissue (follicle) cells, and in this way the rudiments of the ovarian follicles are formed (Fig. 1113). According to Beard the primitive ova are early set apart during the segmentation of the ovum and migrate into the germinal ridge. |
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FIG. 1111– Transverse section of human embryo eight and a half to nine weeks old. (From model by Keibel.) (See enlarged image) |
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FIG. 1112– Longitudinal section of ovary of cat embryo of 9.4 cm. long. Schematic. (After Cœrt.) (See enlarged image) |
| Waldeyer taught that the primitive germ cells are derived from the “germinal epithelium,” covering the genital ridge. Beard, 1 on the other hand, maintains that in the skate they are not derived from this epithelium, but are probably formed during the later stages of cell cleavage, before there is any trace of an embryo; and a similar view was advanced by Nussbaum as to their origin in amphibia. Beard says: “At the close of segmentation many of the future germ cells lie in the segmentation cavity just beneath the site of the future embryo, and there is no doubt they subsequently wander into it.” The germ cells, “after they enter the resting phase, are sharply marked off from the cells of the embryo by entire absence of mitoses among them.” They can be further recognized by their irregular form and ameboid processes, and by |