File:The physiology of domestic animals (1905) (20722806425).jpg

Title: The physiology of domestic animals ..
Identifier: cu31924000350045 (find matches)
Year: 1905 (1900s)
Authors: Smith, Robert Meade, 1854-
Subjects: Physiology, Comparative; Veterinary physiology
Publisher: Chicago, A. Eger
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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REPRODUCTIVE FUNCTIONS. 915 the accompanying diagram (Fig. 415). In man the spermatozoa are about .05 millimeter in length, the head being oval with a thickened posterior border, and their shape is, therefore, somewhat analogous to that of a pear. The spermatozoa are developed from the nucleated protoplasmic cells which line the seminal tubules of the testicle. These tubules are lined by several layers of more or less cubical cells. The outer cells, next the basement membrane, often show a large nucleus in process of subdivision. Internal to these are several layers of inner cells with nuclei, often dividing so that they form a progeny of cells internal to those toward the lumen of the tube. From these cells so formed by sub- division and which are termed spermatoblasts the spermatozoa are formed. These spermatic cells are spindle-shaped and form nucleated protoplasmic prolongations which project into the lumen of the tube and break up at their free ends into flat, round, or oval lobules. During the
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I jy M TL Fig. 416.—Semi-diagkammatic Spebmatogenesis. (Landois.) I. Transverse section of a seminal tubule; a, membrane; 6, protoplasmic inner 1'nlng, <vperma0- blast; l seminal cells. II. Unripe spermatoblast; /, rounded cleavage lobules; p, seminal cells. III. SpermatobS? with a free spermatozoon, I. IV. Spermatoblast, with ripe spermatozoa, 1c, not yet detached; r, tail; n, wall of the seminal tubule; h, its protoplasmic layer. process of development of these spermatoblasts each lobule lengthens into a tail or cilium-like prolongation, while the deeper part still in connection with the walls of the tube will ultimately form the head and middle portion of the spermatozoon: so that in this stage of its develop- ment the sperm is composed of an enlarged.cylindrical cell terminating in cilium-like prolongations. When the development is complete the head becomes detached and the remainder of the spermatoblast under- goes fatty degeneration, although a small amount of the protoplasm may remain temporarily attached to the head of the spermatozoon (Fig. 416). Between the spermatoblasts lining the lumen of the seminal tubules are found numerous round cells possessed of amoeboid movement, the so- called seminal cells, which are probably concerned in the formation of the fluid parts of the semen.

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