HUMAN SPERMATOGENESIS: A STUDY OF INHERITANCE. 15 



begins to elongate, and to enlarge more rapidly than the distal (figs. 57, 58), 

 whereupon both sink inwards to lie against the nucleus (figs. 59, 60) ; this move- 

 ment produces an infundibuliform depression of the cell body out of which the 

 axial filament projects, and this funnel comes later to lie upon one side of the cell 

 (figs. 62-64, 73, 76, 79, 81, 85, 88, 91), and still later to close entirely. The 

 proximal centriole (c.p.) becomes angularly bent, with one end touching the 

 distal, while the latter flattens slightly and then becomes a ring (figs. 60-64). 

 Frequently the proximal lies in such a position as to be hidden by the nucleus. 

 (fig. 66), or so as not to show its angular form (figs. 59, 62, 64, 68). 



From this time on it will be convenient to follow the two centrioles separately. 



The distal centriole is the one that undergoes the fewest changes, It early 

 becomes a small ring with a minute aperture (c.d., fig. 63), and throughout its 

 history appears to remain against the cell membrane. It then increases slowly 

 in size until it attains the diameters shown in figs. 74-91. In one case a granule 

 was observed just distal from it (fig. 82), but whether derived from it I could not 

 ascertain. All through this long period the distal centriole continues in contact 

 with the proximal, and has a lateral position upon the cell. Later the distal 

 centriole moves away from the proximal, and comes to lie some distance behind 

 the nucleus (figs. 93-96, PI. Ill; 97-101, PI. IV). As it moves caudad it becomes 

 smaller, as seen in figs. 99, 100, and in the latest stage in which it was found, fig. 

 101, it was a very small, pale-staining body. On no later stages was any trace 



of it to be observed, so that I cannot say whether it becomes thrown off 

 with the cytoplasm, completely degenerates, or persists, though invisible, in 

 some region of the tail as, e. g., just behind the mitochondrial mantle. 

 Certainly, however, no trace of this centriole is to be observed in the mature 

 spermatozoon. 



The proximal centriole has a more complicated history. It retains for a long 

 while the angular form already described (figs. 58-75), whereby one end touches 

 the nucleus. It lies then very close to the distal centriole and may touch it either 

 at the centre or at the periphery; rarely are the two at this time distinctly sepa- 

 rated, but when they are (fig. 77) the axial filament can be seen connecting them. 

 Then the proximal centriole begins to change its shape, changing from an angular 

 to a curved and then to a rod-like form (figs. 77-81). It afterwards constricts 

 into a smaller anterior portion (c.p., figs. 82-86) and a larger posterior portion 

 (c.p. 2). The anterior portion lies against the nucleus some little distance from 

 its posterior end (figs. 84-86). 



In later stages, as a rule, the anterior portion of the proximal centriole cannot 

 be recognized on account of its close apposition to the nucleus; but occasionally 

 it may be discerned projecting slightly from the nucleus (c.p. 1, figs. 107, 114, 

 PI. IV), and in a single case it was observed very distinctly (fig. 115). The 

 posterior portion remains for awhile quite large (c.p. 2, figs. 88-92), and is con- 

 nected with the nucleus (or rather with the anterior portion at the nucleus) by a 

 deep staining thread of centrosomal substance. Immediately thereafter the 



