MALE ELEMENTS OF GENERATION 



785 



which are the result of the final division, are called spermatocytes. 

 These divide again to form each two spermatids, the number of con- 

 tained chromosomes being thereby reduced one-half, and these sper- 

 matids are developed into spermatozoids, in fan-shaped groups that 

 project into the calibre of the seminiferous tubes. 



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 



Fig. 215. Diagram showing stages of spermatogenesis as seen in different sectors of a seminiferous 

 tubule of a rat (McMurrich, modified from von Lenhossek). 



s, Sertoli cell; sc l , spermatocyte of the first order; stf, spermatocyte of the second order (divided 

 into two) ; sg; spermatogone ; sp, spermatid ; sz, spermatozoids. 



In the first section (to the left) four different generations of cells are shown: sg, spermatogones ; 

 sc l , spermatocytes ; sp, spermatids ; sz, spermatozoids. In the second section are spermatocytes, 

 spermatids, and a Sertoli cell increased in size. In the third section are spermatocytes, sc^ undivided 

 and sc% divided, and a still larger Sertoli cell, with spermatozoids. In the fourth section are the two 

 orders of spermatocytes, spermatids to the right, and a still larger Sertoli cell, with spermatozoids. In 

 the fifth section are four spermatogones in contact with the basement membrane, spermatocytes of 

 the first and second orders, spermatids and a Sertoli cell, with spermatozoids. sz, of the first section, 

 shows spermatozoids lying in the lumen of the tubule. 



vesiculae seminales, and for a certain time after ejaculation, the sperma- 

 tozoids are in active motion. When the spermatozoids have ceased 

 their movements they are incapable of fertilizing 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 innumer- 

 able spermatozoids in active movement ; but if sexual intercourse is 

 frequently repeated at short intervals, the ejaculated liquid becomes 

 more and more transparent, homogeneous and scanty, and it may con- 

 sist of a small quantity of secretion from the vesiculae seminales and 

 the glands opening into the urethra, without spermatozoids and conse- 

 quently deprived of fertilizing power. 



3E 



