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 



I 



jy 



M 



TL 



Fig. 416.— Semi-diagkammatic Spebmatogenesis. (Landois.) 



I. Transverse section of a seminal tubule; a, membrane; 6, protoplasmic inner 1'nlng, <v per ma 0- 

 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. 



