. The cell in development and inheritance. Cells. Fig. 100. — Entrance of the spermatozoon into the egg. A-G. In the sea-urchin, Toxopncusfes. H. In the medusa, Mitrocotna. [MeTSCHNIKOFF.] /. In the star-fish Asterias. [FOL.] A. Spermatozoon of Toxopneustes, X 2000; a. the apical body, n. nucleus, m. middle-piece, f. flagellum. B. Contact with the egg-periphery. C. D. Entrance of the head, formation of the entrance-cone and of the vitelline membrane (v), leaving the tail outside. E. F. Later stages. G. Appearance of the sperm-asler {s) about 3-5 minutes after first contact; entrance-cone break
. The cell in development and inheritance. Cells. Fig. 100. — Entrance of the spermatozoon into the egg. A-G. In the sea-urchin, Toxopncusfes. H. In the medusa, Mitrocotna. [MeTSCHNIKOFF.] /. In the star-fish Asterias. [FOL.] A. Spermatozoon of Toxopneustes, X 2000; a. the apical body, n. nucleus, m. middle-piece, f. flagellum. B. Contact with the egg-periphery. C. D. Entrance of the head, formation of the entrance-cone and of the vitelline membrane (v), leaving the tail outside. E. F. Later stages. G. Appearance of the sperm-asler {s) about 3-5 minutes after first contact; entrance-cone break- ing up. H. Entrance of the spermatozoon into a preformed depression. /. Approach of the spermatozoon, showing the preformed attraction-cone. neck of the archegonium. Those of mosses, on the other hand, are indifferent to malic acid, but are attracted by cane-sugar. These experiments indicate that the specific attraction between the germ- cells of the same species is owing to the presence of specific chemical substances in each case. There is clear evidence, furthermore, that the attractive force is not exerted by the egg-nucleus alone, but by the egg-cytoplasm ; for, as the Hertwigs and others have shown, spermatozoa will readily enter egg-fragments entirely devoid of a nucleus. In naked eggs, such as those of some echinoderms, and coelen- terates, the spermatozoon may enter at any point; but there are some cases in which the point of entrance is predetermined by 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 Wilson, Edmund B. (Edmund Beecher), 1856-1939. New York Macmillan
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1906
