. The cell in development and inheritance. Cells; Cells. Fig. 74. — Entrance of the spermatozoon into the egg. In the sea-urchin ToA-f^j^wf^/jfef. H. In the medusa Mitrocoma. [METSCHNIKOFF.] /. In the star-fish Asterias. [FOL.] A. Spermatozoon of Toxop7ieustes, 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 entfrince-cone and of the vitelline membrane (ti), leaving the tail outside. Later stages. G. Appearance of the sperm-aster {s) about 3-5 minutes after first contact; entrance-
. The cell in development and inheritance. Cells; Cells. Fig. 74. — Entrance of the spermatozoon into the egg. In the sea-urchin ToA-f^j^wf^/jfef. H. In the medusa Mitrocoma. [METSCHNIKOFF.] /. In the star-fish Asterias. [FOL.] A. Spermatozoon of Toxop7ieustes, 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 entfrince-cone and of the vitelline membrane (ti), leaving the tail outside. Later stages. G. Appearance of the sperm-aster {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. ragged flame-shape and breaking up into slender rays. In some cases the ^'g% remains naked, even after fertilization, as appears to be the case in many coelenterates. More commonly a vitelline mem- brane is quickly formed after contact of the spermatozoon, — in AmpJiioxits, in the echinoderms, and in many plants, — and by means of this the entrance of other spermatozoa is prevented. In eggs surrounded by a membrane before fertilization, the spermato- zoon either bores its way through the membrane at any point, as is probably the case with mammals and amphibia, or may make its entrance through a micropyle. In some forms only one spermatozoon normally enters 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 : The Macmillan company
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectcells, bookyear1896
