The development of the human body; a manual of human embryology . , the layerof primary spermatocytes may still be seen, indicationsof an approaching division being furnished by the ar-rangement of the chromatin in those of the second sec-tion, and in the third section the division is seen in pro-gress, the two cells which result from it being termedsecondary spermatocytes (sc2). These cells almost im-mediately undergo division, as shown in the fourth sec-tion, each giving rise to two spermatids (sp), each ofwhich becomes later on directly transformed into a sper-matozoon (sz). From the primar
The development of the human body; a manual of human embryology . , the layerof primary spermatocytes may still be seen, indicationsof an approaching division being furnished by the ar-rangement of the chromatin in those of the second sec-tion, and in the third section the division is seen in pro-gress, the two cells which result from it being termedsecondary spermatocytes (sc2). These cells almost im-mediately undergo division, as shown in the fourth sec-tion, each giving rise to two spermatids (sp), each ofwhich becomes later on directly transformed into a sper-matozoon (sz). From the primary spermatocyte therehave been formed, therefore, as the result of two mi-toses, four cells, each of which represents a these divisions important departures from thetypical method of mitosis occur. These departures SPERMATOGENESIS. 31 have been most thoroughly studied in the lower forms,but it is probable that they are fundamentally similarin the mammalia. It has already been pointed out () that the number of chromosomes which appear dur-. Fig. 7.—Diagram Illustrating the; Reduction of the Chromo-somes During , Spermatocyte of the first order; sc°, spermatocyte of the secondorder; sp, spermatid. ing the mitoses of the somatic cells is characteristic forthe species. In the division of the primary spermato-cytes the number of chromosomes which appear is ap-parently only half the characteristic number, but in real-ity it is double that number, since each chromosome is 3^ THE DEVELOPMENT OF THE HUMAN BODY.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
