i6o2 



A MANUAL OF ANATOMY 



arranged in a lanceolate manner, and forms the perforaculum, which 

 is well adapted for perforating. The head represents the nucleus of 

 the parent-spermatid, the nucleus being elongated and oval. It 

 consists of a dense collection of chromatin, and external to it there is a 

 delicate layer of cytoplasm. The archoplasm of the parent-spermatid 

 gives rise, at the anterior end of the nucleus, to the head-cap. 



The middle piece lies behind the head, and from its posterior end 

 the fiagellum, or tail, is prolonged. The middle piece is developed 

 from the cytoplasm of the parent-spermatid. It contains a ceniro- 

 some, which is situated near the head. 



The flagellum or tail, is the slender filament of lashing move- 

 ment, and is much elongated. It consists of a central fibril, or axial 

 filament, which is prolonged from the centrosome in the middle 

 piece. The filament is surrounded by a delicate sheath, which dis- 

 appears towards the end of the tail. The relation of a spermatozoon 

 to its parent-spermatid may be stated as follows : 



Spermatozoon. 

 Head 

 Head-cap 

 Middle Piece 

 Flagellum or Tall 



Parent-Spermatid. 

 Nucleus. 

 Archoplasm. 

 Cytoplasm. 

 Centrosome and Cytoplasm. 



Spermatogenesis. 



Spermatogenesis is the begetting 

 formed in immense numbers within 



Primordial Germ-cell 



of spermatozoa, which are 

 the tubuli seminiferi of the 

 testes. Each . spermatozoon 

 is developed from the ger- 

 minal epithelium, its original 

 source being known as the 

 primordial germ- or sperm- 

 cell, which is of large size. 

 These cells undergo several 

 mitotic divisions, and from 

 the last generation spermato- 

 gonia are developed, which 

 correspond to the oogonia of 

 the female. These spermato- 

 gonia divide, by mitosis, and 

 give rise to primary spermato- 

 cytes, two for each spermato- 

 gonium, and these corre- 

 spond to the female primary 

 oocytes. Each primary sper- 

 matocyte divides, by mitosis, 

 into two cells, which are 

 known as the secondary sper- 

 matocytes, and correspond to 

 the female secondary oocytes. 

 Each secondary spermatocyte, in turn, divides, by mitosis, into two 

 cells, which are called spermatids, and each of these corresponds 



Primary Spermatocyte - 



Secondary 

 Spermatocyte— -fl^ )t 



, Division- 

 Period 



.Growth- 

 Period 



Fig 



Spermatid d V 4 ▼ 



Spermatozoa, _..^ i i i 

 659. — Diagram showing Spermato 



GENESIS (after BoVERI). 



Maturation- 

 Period 



