152 THE DEVELOPMENT OF THE GAMETES OR SEX CELLS 



with centriole 1 (fig. 80G, post-nuclear membrane). This membrane grows 

 anteriad to meet the acrosomal cap (fig. 81A-C). In the sperm of the guinea 

 pig, a series of post-nuclear granules in the early spermatid appear to coalesce 

 to form the post-nuclear cap (fig. 82A-C). 



c) Formation of the Proximal and Distal Centrioles; Axial Fila- 

 ment. While the above changes in the formation of the acrosome are pro- 

 gressing, the centriole (or centrioles) of the idiosome move to the opposite 

 side of the nucleus from that occupied by the forming acrosome, and here 

 in this position the proximal and distal centrioles of the future sperm arise. 

 In this area the neck granules also make their appearance (figs. 68B; 80F-H). 

 The axial filament arises at this time and it probably is derived from the two 

 centrioles simultaneously (fig. 80F, H). The centrioles soon become displaced 

 along the axial filament, the caudal end of which projects from the surface 

 of the cell membrane (fig. 80F-H). The axial filament grows outward pos- 

 teriorly from the cell membrane in line with the two centrioles and the 

 acrosome-forming material. The anterior-posterior elongation of the sperm 

 thus begins to make its appearance (fig. 80H). The anterior centriole retains 

 a position close to the nuclear membrane, but the posterior or ring centriole 

 moves gradually posteriad toward the cell surface (figs. 81, 82A-C). 



d) Mitochondrial Material and Formation of the Middle Piece 

 OF the Sperm. The behavior of the mitochondria in the formation of sperm 

 varies greatly. In the spatulate sperm described above, a portion of the mito- 

 chondrial substance becomes aggregated around the axial filament in the 

 middle-piece area (figs. 77, 82D). In certain amphibian sperm the middle 

 piece appears to be formed mainly by centrioles 1 and 2 (fig. 79D-F). In 

 certain insects the mitochondrial body or nebenkern, divides into two masses 

 which become extended into elongated bodies associated with the flagellum 

 (fig. 84). Some of the mitochondrial substance is discarded with the Golgi 

 substance and excess cytoplasmic materials. 



e) The Cytoplasm, Axial Filament, Mitochondria, and Tail For- 

 mation. Synchronized with the above events, the cytoplasm becomes drawn 

 out in the posterior direction, forming a thin cytoplasmic layer over the sperm 

 head, and from thence posteriad over the middle piece and the chief piece 

 of the flagellum. However, the end piece of the flagellum may be devoid of 

 investing cytoplasm (fig. 77). As the cytoplasm is elongating posteriorly over 

 the contained essential structures of the forming sperm, much of the cytoplasm 

 and Golgi substance and some mitochondria are discarded and lost from the 

 sperm body. It may be that these discarded bodies form a part of the essential 

 substances of the spermatic (seminal) fluid. (See Chap. 1.) (See figs. 66; 

 68B-E; 81; 82; 85M-0.) 



The centralized core of the tail is the axial filament which arises in relation 

 to centrioles 1 and 2 and grows posteriad through the middle piece and tail 



