XIl] THE MALE GENERATIVE ORGANS 1 53 



have a nourishing and supporting function. Oil the inside of the 

 spermatogonia are certain larger cells known as spermatocytes. 

 They are the products of division of the spermatogonia. On the 

 inside of the spermatocytes are the spermatids which are derived 

 from the speimatocytes by cell division. The spermatids in many 

 cases become elongated and converted into spermatozoa. A small 

 quantity of fluid is secreted into the testicular luniina, but it does 

 not appear to be certain as to what cells are especially concerned 

 in this secretion. 



A fully developed spermatozoon consists of an egg-shai^ed 

 head which rejjresents the cell 



nucleus, a short cylindrical body or Q * - • " 



middle piece, and long delicate vibra- pjg 75 spermatozoon of ram 

 tile tail, by means of which the sperm (^^m Marshall), 



is propelled forwards. 



In the process of spermatogenesis the quantity of luiclear 

 material (as shown by the number of chromosomes or filaments 

 ^\"hich go to compose the nuclear material) in each final product 

 of division (i.e. in each spermatozoon) is reduced to one-half of 

 the normal amovnit characteristic of the cells in the species in 

 question. Thus in the horse the normal number of chromosomes 

 for all the cells of the body' excepting the mature reproductive 

 cells is 26, whereas the number of chromosomes in the sperma- 

 tozoon of the horse is 13. This is due to the fact that m the last 

 cell division but one leading up to spermatogenesis the chromo- 

 somes do not undergo the splitting which universally characterises 

 cell-division excepting in the reduction processes of the repro- 

 ductiv^e cells. In the final division the chromo.somes split as usual. 

 The nuclear material in the matvire ovum is also reduced by half, 

 so that in the act of fertilisation when the ovum and spermatozoon 

 unite the number of chromosomes becomes once more restored to 

 the normal amount characteristic of the species. 



The efferent ducts of the testis or vasa efferentia (about twelve 

 in number) open into a single convoluted tube situated at the 

 posterior end of the testis. This is the epididymis. It is lined 

 internally by a columnar, ciliated epithelium which is believed to 

 have some secretorj^ activity. The epididymis serves mainly as 

 a storehouse for the spermatozoa prior to seminal ejaculation. 

 Smooth muscle fibres are present in its walls as \\ell as in those 

 of the vasa efferentia. 



