STKUCTURE OF THE SEMINIFEROUS TUBES. 



557 



The contents of the seminal tubes vary according to age. Pre- 

 viously to puberty, they contain nothing but minute clear cells, 

 resembling epithelial cells. At this period, however, the tubes 

 increase in size, and when the formation of semen has commenced, 

 they become clear, round cells and cysts, 3^3 to 4^ of an inch in 

 diameter, inclosing from 1 to 10, or even 20, clear nucleolated 

 nuclei, ^^ to -^Vu of an inch in diameter. At this time, also, 

 the epithelium is not manifest, the cells in question appearing en- 

 tirely to fill the tubes (Fig. 386); though at other times, especially 



Fig. 386. 



Seminal tube (man), with contained cells, a. Wall of tube. b. Nuclei of fibrous coat. c. Base- 

 ment-membrane, d. Cells removed from the tube. The latter figure shows the action of acetic acid. 

 (Magnified 220 diameters.) 



in advanced years, the epithelium appears, containing fat, or pig- 

 ment-cells, surrounding the other elements. The cells and cysts 

 (spermatophori) just mentioned are the precursors of the semen; 

 for in each nucleus a spermatic filament (spermatozoid) is developed 

 on the inner wall, as a spiral corpuscle with two or three turns. 

 (Figs. 387 and 117.) This development commences in the tubuli testis, 

 but it is not completed so that the spermatozoids become liberated, 

 till they reach the rete testis and the coni vasculosi. The nuclei 

 first bursting, the spermatozoids remain for a time in the cysts or 

 spermatophori, the heads and tails together when numerous (10 to 

 20); but subsequently the spermatophori also burst, in the epididy- 

 mis, and the dense entangled crowd thus liberated entirely fill its 



