MALE ORGANS OF REPRODUCTION 



485 



cells involved in spermatogenesis. As concerns details, the criteria 

 above given for the grasshopper testis, can be applied. 



The Spermatozoon. Spermiohistogenesis, however, differs some- 

 what. The spermatid nucleus becomes progressively more compact, 

 chromatic and smaller. At the same 

 time it moves toward one pole of the 

 cell, the cytoplasm flowing back- 

 ward, except for a thin envelope 

 (irulca capitis) which terminally 

 forms a covering for the perfora- 

 torium which represents a portion 

 (acrosome) of the original idiosome. 

 The idiosome is the germ-cell repre- 

 sentative of the archoplasmic com- 

 plex. Concurrently with the changes 

 outlined for the nucleus it liberates 

 a centrosome, and centrosome and 

 acrosome pass to opposite poles of 

 the nucleus. The centrosome di- 

 vides into two moieties, a proximal, 

 which becomes attached to the nu- 

 clear membrane, and a distal, which 

 moves peripherally at the same time 

 sprouting a flagellum, the central 

 filament. Meanwhile a peripheral 

 portion separates from the more 

 central portion of the distal centro- 

 some and moves backward over the 

 central filament enclosing an envel- 

 oping column of cytoplasm, the mid- 

 dle piece, in which mitochondria 

 have aggregated. The mitochondria 

 fuse to form a filament, the spiral 

 fUtinic.nt, which becomes spirally ar- 

 ranged about the central filament, 

 grow distally beyond the final locus of the ring centrosome, and together 

 with an envelope of cytoplasm constitutes the tail of the spermatozoon. 

 A short terminal naked portion of the central filament is known as the 

 terminal filament. 



Summarizing the above: The nucleus becomes the head of the 



Main segment of 

 tail 



Oalea capitis 



-- Spiral fibers 



... Sheath of axial 

 thread 



- Axial thread 



Capsule 



Terminal filament . 



FIG. 430. DIAGRAM OF HUMAN SPER- 

 MATOZOON. 



(After Bonnet.) 



The central filament continues to 



