886 



GENERATION. 



occurs that, when from ten to twenty spermatozoids are developed in a single vesicle, the 

 heads and tails are arranged regularly, side by side ; but, when only two or three are ob- 

 served, their arrangement is irregular. The vesicular envelopes finally disappear and the 

 spermatozoids are liberated ; but this occurs only in the rete testis and in the epididymis. 

 In the epididymis and the vasa deferentia, the spermatozoids are motionless, though they 

 are not enclosed in vesicles, apparently from 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 saline solutions. Once in the 

 vesiculse seininales, or after ejaculation, the spermatozoids are invariably in active motion. 



Fie. 285. Development of the spermatozoids in the rabMt. (Liegeois.) 



a, a, spermatozoids ; ft, spermatic cell containing thirteen nuclei, two of which contain each a head of a spermatozoid 

 developed; c, spermatic cell containing two secondary cells, each one provided with a nucleus from which two 

 epermatozoids are to be developed ; ef,/, spermatic cells, each with one nucleus; , spermatic cell containing a 

 secondary cell with a nucleus ; A, bundle of spermatozoids. 



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

 found during adult life and even at an advanced age ; and, under physiological condi- 

 tions, it contains innumerable spermatozoids in active movement. But if sexual inter- 

 course be frequently repeated at short intervals, the ejaculated fluid becomes more and 

 more transparent, homogeneous, and scanty, and it may consist of a small amount of secre- 

 tion from the vesiculse seminales and the glands opening into the urethra, without sper- 

 matozoids, and consequently deprived of fecundating properties. 



In old men, the seminal vesicles may not contain spermatozoids ; but this is not always 

 the case, even in very advanced life. Instances are constantly occurring of men who 

 have children in their old age, in which the paternity of the offspring can hardly be 

 doubted. Duplay, in 1852, examined the semen of a number of old men, and found, in 

 about half the number, spermatozoids, normal in appearance and quantity, though, in 

 some, the vesiculse seminales contained either none or very few. Some of the individu- 

 als in whom the spermatozoids were normal were between seventy-three and eighty-two 

 years of age. More recently, M. A. Dieu has investigated the same question. In his 

 conclusions, adding to his own observations the fifty-one cases noted by Duplay, he gives 

 the following results, in one hundred and fifty-six old men : 



" 25 sexagenarians gave a proportion, still presenting spermatozoids, of 68'5 per 100. 



