The development of the human body; a manual of human embryology . , tail; w, middle-piece.{After Retzius.) Fig. 5.—Spermatozoon op , Head; he, head-cap; mp, mid-dle-piece; n, neck.—{Jensen.) and the head-cap undoubtedly exists in the earlier stages ofthe development of the spermatozoon, though it may later belost. To understand the significance of the various partsentering into the composition of the spermatozoon astudy of their development is necessary, and since thevarious processes of spermatogenesis have been muchmore accurately observed in such mammalia as the rat SPERMATOGENESIS. 29
The development of the human body; a manual of human embryology . , tail; w, middle-piece.{After Retzius.) Fig. 5.—Spermatozoon op , Head; he, head-cap; mp, mid-dle-piece; n, neck.—{Jensen.) and the head-cap undoubtedly exists in the earlier stages ofthe development of the spermatozoon, though it may later belost. To understand the significance of the various partsentering into the composition of the spermatozoon astudy of their development is necessary, and since thevarious processes of spermatogenesis have been muchmore accurately observed in such mammalia as the rat SPERMATOGENESIS. 29 and guinea-pig than in man, the description which fol-lows will be based on what has been described as occur-ring in these forms. From what is known of the sperma-togenesis in man it seems certain that it closely resemblesthat of these mammals so far as its essential features areconcerned. Spermatogenesis.—The spermatozoa are developed fromthe cells which line the interior of the seminiferous tubulesof the testis. The various stages of development cannot. Fig. 6.—Diagram showing Stages op Spermatogenesis as seen in Different Sectors of a Seminiferous Tubule of a , Sertoli cell; sc1, spermatocyte of the first order; sc2, spermatocyte of• the second order; sg, spermatogone; sp, spermatid; sz, spermato-zoon —(Modified from von Lenhossek.) all be seen at any one part of a tubule, but the formationof the spermatozoa seems to pass along each tubule ina wave-like manner and the appearances presented atdifferent points of the wave may be represented diagram-matically as in Fig. 6. In the first section of this figure four different genera-tions of cells are represented; above are mature sperma-tozoa lying in the lumen of the tubule, while next the 30 THE DEVELOPMENT OF THE HUMAN BODY. basement membrane is a series of cells from which a newgeneration of spermatozoa is about to develop. Thecells of this series are of two kinds; the larger one (s)will develop into a struc
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
