THE TESTES. 



1945 



end of the cell most removed 

 from the lumen. The modified 

 spermatids now become closely 

 related with a Sertoli cell, with 

 the protoplasm of which they 

 fuse. The structure thus 

 formed, known as the sperma- 

 toblast, consists of an irregular 

 nucleated conical protoplas- 

 mic mass (Fig. 1657, 27), 

 with the inner end of which the 

 radiating clusters of partially 

 fused spermatids are blended. 

 The succeeding changes in- 

 clude the transformation of the 

 elongated nucleus of the sper- 

 matid into the head and of its 

 centrosome into the neck- 

 granules of the spermatozoon, 

 while from the protoplasm of 

 the spermatid, possibly in con- 

 junction with that of the sper- 

 matoblast, the flagellate tail- 

 filament is derived. As the 

 spermatozoa become more 

 and more differentiated, they 

 appear as fan-shaped groups 

 in which the heads are always 

 buried within the spermato- 

 blast and the tails directed to- 

 wards the lumen of the canal. 

 After separation, which subse- 

 quently takes place, the liber- 

 ated spermatozoa occupy the 

 centre of the tubule as masses 

 which often occlude its lumen 

 and in which the seminal fila- 

 ments are disposed in peculiar 

 whorl-like groups. Their com- 

 plete development, however, 

 is deferred until they reach 

 the tube of the epididymis, 

 during the passage through 

 which highly tortuous path 

 they attain maturity and lose 

 the protoplasmic remains of 

 the spermatids that usually for 

 a time adhere to the middle- 

 piece. The spermatogenetic 

 process does not involve uni- 

 formly all parts of the seminif- 

 erous tubule, but is manifested 

 with wave -like periodicity ; 

 consequently sections taken 

 through the same tubule a few 

 millimetres apart exhibit dif- 

 ferent stages of the cycle, al- 

 though the cells are never all 

 of one phase. 



FIG. 1655. 



Dilated duct 



Blood-vessel 



Part of mediastinum, showing; irregular channels of rete testis. X 75- 



FIG. 1656. 



Tunica propria 



Secondary spermatocyte 

 Spermatids 



Spermatids being 

 transformed into spermatozoa 



Secondary spermatocyte 

 Spermatozoa 



- -\JJ v ', - i v,i -iv , : . 'M7 ; \', ' 



_."^-,>^;^v/// ,'///' 



I ..AI&J 



Sertoli cell 

 Resting spermatogone 



>goiie 



Dividing spermatogone (primary spermatocyte) 



Portion of seminiferous tubule, cut transversely, showing lining 

 cells in various stages of spermatogenesis. X 350. 



