T92 



GENERATION. 



tozoids, which may be restored by the addition of dense saline and other 

 solutions. All of the alkaline, animal fluids of moderate viscidity favor the 

 movements, while the action of acid or of very dilute solutions is unfavorable. 

 The movements are suspended by extreme cold, but they return when the 

 ordinary temperature is restored. 



Before the age of puberty the seminiferous tubes are much smaller than 

 in the adult, and they contain small, transparent cells, which in their form 

 and arrangement resemble epithelium. As puberty approaches, however, 

 the tubes become larger, and the contents change their character. The walls 

 are then provided with spindle-shaped cells with a nucleated, protoplasmic 

 lining, sending prolongations into the interior of the tube. These prolonga- 

 tions afterward break up into little, rounded bodies called spermatoblasts, a 

 part of each one of which becomes the head of a spermatozoid (Ebner). 

 Between the prolongations, are the so-called spermatic cells. The spermato- 

 blasts send out each one a short process which forms the intermediate seg- 



III 



FIG. 290.Spermatogenesis ; semi-diagrammatic (Landois). 

 I, transverse section of a seminal tubule ; A, external membrane ; B, protoplasmic lining ; c, sperma- 



toblast ; s, seminal cells. 

 II, projection with F, spermatoblasts ; s, seminal cells. 



III, spermatoblasts with spermatozoids not yet detached. 



IV, spermatoblasts with a spermatozoid detached. 



ment of the spermatozoid, and from this a long filament is developed, which 

 forms the tail. The spermatozoid is detached when its development is complete. 



The spermatozoids are motionless while they are within the testicle, the 

 epididymis or the vasa deferentia, apparently on account of the density of 

 the substance in which they are embedded ; for movements are sometimes 

 presented when the contents of the vasa deferentia are examined with the 

 addition of water or of saline solutions. Once in the vesiculae seminales, and 

 for a certain time after ejaculation, the spermatozoids are in active motion. 

 When the spermatozoids have ceased their movements they are incapable 

 of fecundating the ovum. 



The semen, thus developed and mixed with the various secretions before 

 mentioned, is found during adult life and sometimes even in advanced age, 

 and under physiological conditions it contains innumerable spermatozoiJs 

 in active movement; but if sexual intercourse be frequently repeated at 

 short intervals, the ejaculated fluid becomes more and more transparent, 



