. Elementary text-book of zoology. Zoology. FERTILIZATION. the protoplasm of the ovum, is thrown out of the egg as the so-called directive bodies or polar cells (tig. 101). The part of it, however, which remains in the ovum retains its significance as a nucleus, and is known as the female pronucleus. This fuses with the single spermatozoon (male pronucleus) which has forced its way into the ovum (fig. 102); and the compound structure so formed constitutes the nucleus of the fertilized ovum, or as it is generally called, the first segmentation nucleus. <~y / N. : ii -jj /. FIG. 103.—Developm
. Elementary text-book of zoology. Zoology. FERTILIZATION. the protoplasm of the ovum, is thrown out of the egg as the so-called directive bodies or polar cells (tig. 101). The part of it, however, which remains in the ovum retains its significance as a nucleus, and is known as the female pronucleus. This fuses with the single spermatozoon (male pronucleus) which has forced its way into the ovum (fig. 102); and the compound structure so formed constitutes the nucleus of the fertilized ovum, or as it is generally called, the first segmentation nucleus. <~y / N. : ii -jj /. FIG. 103.—Development of a Star-fish, Asteracanthion berylinus (after Alex. Agass'z). 1, Commencing segmentation of the flattened egg—at one pole are seen the polar bodies; 2, stage with two segments ; 3, with four ; 4, with eight; 5, with thirty-two segments ; G, later stage; 7, blastosphere with commencing imagination; 8 and 9, more advanced stages of iuvagination. The opening of the gastrula cavity becomes the anus. This new nucleus, which divides to give rise to the nuclei of the first segmentation spheres, would appear therefore to be the product of the fusion or conjugation of the part of the germinal vesicle, which remains behind in the ovum, with the male pronucleus, which is a derivative of the spermatozoon which has entered the ovum. Fertilization u-oidd appear, therefore, to depend upon the addition. 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 Claus, Carl, 1835-1899; Sedgwick, Adam, 1854-1913; Sinclair, F. G. (Frederick Granville), b. 1858. New York : Macmillan
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
