SPERMATOGENESIS 



distinctive nuclear characters the spermatogonia. These divide rapidly for a 

 time, then cease to multiply and give rise to a new generation of cells the 

 spermatocytes. In this generation a series of changes in the nucleus is effected which 



are of profound significance, and will 

 be described later. Gradually en- 

 larging, the spermatocytes divide into 

 rather smaller elements, the spermato- 

 cytes of the second order, which in turn 

 again divide to form the spermatids. 

 It will thus be seen that from each 

 spermatogonium, by two successive 

 divisions, four equivalent spermatids 

 are formed. Each member of this 

 group of four becomes, by further 

 changes, a spermatozoon. The sper- 

 matids lie near the lumen of the 

 tubules, and become attached to certain 

 remarkable elongated striated cells 

 known as the cells of Sertoli, or foot- 

 cells. The spermatids have meanwhile 

 acquired flagella, and remain attached 

 to the foot- cells in groups, becoming 

 gradually converted into the young 

 spermatozoa, which lie in groups with 

 their tails gathered into the lumen of 

 the tubule. When mature, the sper- 

 matozoa are set free in the tubule by 

 losing their connexion with the foot- 

 cells, which then shrink back to the wall 

 of the tubule. 



The process of metamorphosis of 

 spermatid into spermatozoon is one of 

 much complexity, by which the nucleus 

 becomes the head, while the protoplasm 

 is reduced to a rudiment in the middle 

 piece. The mitochondria of the sper- 

 matid have been shown by Benda and 

 Meves to give origin to the spiral fila- 

 ment. Of the two centrosomes of the 

 spermatid, one remains as an indepen- 

 dent body, while the other becomes 

 related to the nagellum, and the 

 attraction-sphere (idiosome) undergoes remarkable changes to form the cap. 



The accompanying diagrams (fig. 14), founded on drawings and descriptions 

 by Meves and by Moore and Walker, 1 will convey a general impression of the 

 process of histogenesis leading to the evolution of the spermatozoon. 



1 Reports of Thompson-Yates and Johnstone Laboratories, University of Liverpool, No. VII. 

 Part I. 1906. For earlier papers by Ballowitz, Bardeleben, Lenhossek, Benda, Meves, Moore, Ebner, 

 Begaud Wilcox, and others, on. mammalian and human spermatogenesis, see Hertwig, Handbuch der 

 Entwickelungsgeschichte, Literature, i. 431 seq. In the matter of structure see also Betzius, Biolog. 

 Untersuch., Neue Folge, x. 1902 ; Broman, Anat. Anzeiger. xxi.; Wederhake, ibid, xxvii. 



FIG, 12. HUMAN SPEBMATOZOA. (Broman.) 



a and b represent spermatozoa in face (in 

 different foci), c and d in profile view. 



