. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 48 IN VERTEBRATE MORPUOLOG Y. The trausforniation of the germ-cells present iu an em bryo into spermatozoa is usually a somewhat complicated process. In the liouud-worm Asians, iu which it retains somewhat primitive characters, the process closely resem- bles what takes place during the maturation of the ovum». Fig. 23.—Diaohams to ,u8tratk the .Matuhation of the Spkum-cell. A — liivisioii of tlie spermogoue. B — (livisiou of the two speruiocytes. C = the four sperm
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 48 IN VERTEBRATE MORPUOLOG Y. The trausforniation of the germ-cells present iu an em bryo into spermatozoa is usually a somewhat complicated process. In the liouud-worm Asians, iu which it retains somewhat primitive characters, the process closely resem- bles what takes place during the maturation of the ovum». Fig. 23.—Diaohams to ,u8tratk the .Matuhation of the Spkum-cell. A — liivisioii of tlie spermogoue. B — (livisiou of the two speruiocytes. C = the four spermatids. D, E — conversion of a spcrniaiid into a spcrniiitozoon. F — fully (levt'loped speiinalozoon. The embryonic germ-cells {spermatogones, Fig. 22, A) undergo karyokiuetic division, the number of chromosomes being, as in the ovum in the division which results iu the formation of the tirst polar globule, twice that which is characteristic for ;e species. Tliey do not undergo longitudinal division, and one half of them passes into one of the daughter cells {spcr- iiKiforyft's) and tlie other half into the otlier, so that these two cells possess the numl)er of chromosomes characteristic for tlie species. A division of these daughter cells (Fig. 22, />') immedial'ilv takes place without a return to the resting stage, nnd uuacc(uipanied by a longitudinal division of the chromo- Hcunes, so that four cells {sfM'i'nudids, Fig. 22, C) are formed, each of which contains only half the ty]ucal number of cliro- jjj(-ya(-)jj5P,ij • one of these cells becomes a s')erm;il'i- zoou. This process is comparable step by step with 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 McMurrich, J. Playfair (James Playfair), 1859-1939. New York : H. Holt
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
