HUMAN SPERMATOGENESIS: A STUDY OF INHERITANCE. 



16 



posterior portion becomes much smaller and moves close to the nucleus (cp. 2, 

 fiaf 87 93-96) Sometimes this portion comes to actually touch the nucleus 

 S' 94) but as a rule it remains separated from it by a clear area, the neck. 

 For some time this posterior portion of the ^^^^^^^^ 

 rounded body, though staining faintly (cp. 2, figs 97, 99, 100, 103, 106, where 

 it should not have been drawn deep black), but in the mature sperm it becomes a 

 narrow line or disc bounding the posterior border o the neck Thus fig 101, 

 cp 2 shows it as a minute spherule, and figs. 105, 107-112, 114 as a dark line 

 at the anterior border of the mitochondrial mantle 



The neck (collum) of the spermatozoon is then the region between the nucleus 

 and the mitochondrial mantle. Its details are seen most distinctly in fig. 115; 

 here the neck is composed of a homogeneous non-staining part between the 

 anterior portion (cp. 1) of the proximal centriole in front, and the posterior 

 part (cp. 2) of this centriole behind. Lying as it does between these two parts, 

 the intermediate clear substance should be considered a differentiation of the 

 original centrodesmosis shown in figs. 82-92, PL III. No fibrous structures 



could be seen within the neck. 



The flagellum arises first in the spermatids in connection with the centrioles. 

 The earliest appearance found is shown in fig. 57, PI. III. It grows rapidly 

 in length, as shown in fig. 59, and none of the other figures of this plate show 

 it in its fullest extent. At first it appears to be connected only with the distal 

 centriole, but when this becomes a ring the flagellum appears to pass through it 

 to join also the proximal centriole (figs. 77, 86). After the proximal centriole 

 has constricted into its two moieties the flagellum is much thicker than before 

 (figs. 90, 93-96), and with the migration of the distal centrosome away from the 

 proximal is clearly seen to extend all the way between the two. When thickened 

 it may be called the axial thread. 



The cell body of the spermatid is at first rounded (figs. 56, 57, 59, PI. HI), 

 but in these early stages frequently exhibits slender extensions (figs. 58, 60) 

 which may be movable pseudopodia such as those seen by me (1911) in life 



Euschistus. Lengthening of the cell body accompanies lengthening of the 



nucleus (figs. 61-96). Thereby most of the cytoplasm comes to lie behind the 

 nucleus and leaves only a thin mantle around the latter, though no precise regu- 

 larity is to be observed in these movements. Very frequently the cell membrane 

 becomes indrawn around the annular girdle of the head, so as to make a small 

 mass of cytoplasm around the anterior portion of the head separated from a 

 larger mass around the posterior portion (figs. 74, 76, 77, 81, 92, 93, 96) ; the cell 

 membrane of the anterior mass usually appears thicker and more refractive. 

 Then follows the abstriction from the spermatozoon of the greater amount ot 

 the cytoplasm, various stages of which process are delineated in figs. 72, 76, 88-9o, 

 PL III; 98-106, 114, PL IV). During this abstriction darkly-stained granules 

 and threads appear in the cytoplasm, probably derived in part from the degener- 

 ating cuff. All the cytoplasm does not generally fall off in a single piece, but 



