. Darwin, and after Darwin. An exposition of the Darwinian theory and a discussion of post-Darwinian questions. Evolution; Heredity. Embryology. 127 observers to take place also from the male germ-cell, or spermatozoon, at or about the close of its develop- ment. The theories to which these facts have given rise will be considered in future chapters on Heredity. Turning now to the mechanism of fertilization, the diagrams (Figs. 34, ^th) represent what happens in the case of star-fish. The sperm-cell, or spermatozoon, is seen in the act of penetrating the ovum. In the first figure it has alread
. Darwin, and after Darwin. An exposition of the Darwinian theory and a discussion of post-Darwinian questions. Evolution; Heredity. Embryology. 127 observers to take place also from the male germ-cell, or spermatozoon, at or about the close of its develop- ment. The theories to which these facts have given rise will be considered in future chapters on Heredity. Turning now to the mechanism of fertilization, the diagrams (Figs. 34, ^th) represent what happens in the case of star-fish. The sperm-cell, or spermatozoon, is seen in the act of penetrating the ovum. In the first figure it has already pierced the mucilaginous coat of the ovum,. Fig. 35.—Fertilization of the ovum of a star-fish. (From the Encycl. Brit, after Fol.) A, spermatozoa in the mucilaginous coat of the ovum ; a prominence is rising from the surface of the ovum towards a spermatozoon ; B, they have nlmost met; C, they have met; D, the .spermatozoon enters the ovum through a distinct opening ; H, the entire ovum, showing extruded polar bodies on its upper surface, and the moving together of the male and female pronuclei; E, F, G, meeting and coalescence of the pronuclei, the limit of which is represented by a line through which the tail of the spermatozoon is passing: the head of the spermatozoon is just entering the ovum proper. It may be noted that, in the case of many animals, the general protoplasm of the ovum becomes aware, so to speak, of the approach of a spermatozoon, and sends up a process to meet it. (Fig. '^^, A, B, C.) Several—or even many—spermatozoa may thus enter the coat of the ovum ; but normally only one proceeds further, or right into the substance of the ovum, for the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Romanes, George John, 1848-1894. Chicago The Open Court Pub. Co
Size: 2820px × 886px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublish, booksubjectheredity
