550 



SPERMATOGENESIS 



the sperm (f, g), while the nucleus becomes its more or less 

 spindle-shaped head and the centrosome takes the form of a 

 small intermediate piece at the junction of head and tail. 

 Thus the sperm or male gamete is a true cell, specially 



I'll-.. 139. — Speiiiiatoiifjii'isih ill lliu .Mi-iIu-CiilLcL (diylioliiipn). 

 A, primitive '^e\-ccll, jiiht preparatory to tlivi>ion, showmi; twtlMj tJiromo>uinrs 

 {t/ir); f. tlie centrosome. B, spurm-niother-cell, formed hy tlie division of A, 

 and cutaining t\vunty-f):>ui chromosomes ; tlie centrosnine lias di\ided into Iwo. 

 C, the b-perm-inolher-cell has divided into two liy a reduLing division, each 

 daiighiri-cell containing twelve chLontosomes, I', e.K.h chuichlei -cell hasdivided 

 again in the same manner, a gioiip of fom spLuu-cells heing produced, each 

 with six chromosomes. E, a single sperm-cell ahont to elnngate to form a speim. 

 V, immature -pcim ; the six chromosomes are still \isible in the head. C, fully 

 foimed sperm. (Fiom Parker's Biology, after vom Ralh.) 



niodificd in most cases for active movement. This actively 

 motile, tailed form is, however, by no means essential : in 



