126 THE GERM-CELLS 



somes of the spermatid-nucleus, (c) a ring-shaped structure staining 

 purple with gentian violet, like the chromatin. The colourless sphere 

 ultimately vanishes, the red rounded body gives rise to the middle- 

 piece, while the ring gives rise to the envelope (fin) of the flagellum. 

 The apex or spur is developed from the nuclear membrane. 1 Her- 

 mann's results on the mouse agree in a general way with those 

 on the salamander ; but the apex (head-cap) is here derived from 

 the cytoplasm. A " Nebenkorper" lies in the cytoplasm, consisting 

 of a pale sphere and a smaller deeply staining body. From the 

 latter arises the " end-knob," which Hermann accordingly homolo- 

 gizes with the middle-piece of the salamander spermatozoon, and 

 from it the axial filament appears to grow out into the flagellum. 

 The colourless sphere disappears as in the salamander, and the 

 envelope of the axial filament is derived from the cytoplasm. Moore 

 ('95) describes the flagellum of elasmobranchs as growing out from 

 the attraction-sphere (archoplasm) of the spermatid (Fig. 62, A). 



Summary. The foregoing account shows that our positive know- 

 ledge of the formation of the spermatozoon still rests upon a some- 

 what slender basis. But despite the discrepancies in existing 

 accounts, all agree that the spermatozoon arises by a direct meta- 

 morphosis of the spermatid, receiving from it a nucleus and a 

 small amount of cytoplasm containing a centrosome or attraction- 

 sphere. All agree, further, that the middle-piece is of archoplasmic 

 origin, being derived, according to some authors, from a true attrac- 

 tion-sphere (or centrosome); according to others, from a " Neben- 

 kern" formed from the spindle-fibres. The former account of its 

 origin is certainly true in some cases. The latter cannot be accepted 

 without reinvestigation, since it stands in contradiction to what is 

 known of the middle-piece in fertilization, and is possibly due to 

 a confusion between attraction-sphere and " Nebenkern." Similar 

 doubts exist in regard to the origin of the apex, which is variously 

 described as arising from the nuclear membrane, from the general 

 cytoplasm, from the " Nebenkern," and from the centrosome. 



Most late observers agree, further, that the flagellum is developed 

 in intimate relation with the archoplasmic material (attraction-sphere 

 or " Nebenkern "). This conclusion tallies with that of Strasburger, 

 who regards the flagella of plant-spermatozoids as derived from the 

 " kinoplasm " (archoplasm), and it is of especial interest in view of 

 Van Beneden's hypothesis of the contractility of the archoplasm- 

 fibrillae. It is, however, possible that the axial filament may be 

 derived from the nucleus, in which case it would have an origin 

 comparable with that of the spindle-fibres in many forms of mitosis. 



1 Hemming described the middle-piece as arising inside the nucleus ; but Hermann's 

 observations leave no doubt that this was an error. 



