The cells, up to the stage of figs. 13 or 14, have been scattered
promiscuously through the cyst; but as the cell begins to elongate,
the one end becomes the anterior-nuclear end, and it shifts to the
periphery of the cyst. The central part of the cyst now shows the
so-called central lumen. As the lengthening goes on the heads of
the forming spermatozoa are all turned toward the distal end of the
cyst. The cyst becomes very narrow and long, apparently preparing
to contain the long, slender spermatozoa. Near the rachis the
spermatozoa seem much twisted, and I surmise that they turn so as to
have the head foremost when set free into the _vas deferens_. Fig. 42
may indicate some such behavior.
(_c_) THE SPERMATOZOON.
The mature spermatozoon consists: (1) of a sharp, spear-like
point; (2) a tube-like head about .02 mm. long, composed of a
densely staining outer wall and a clearer central cavity; and (3)
a filamentous tail about .5 mm. long. The point comes from the
acrosome, the head from the nucleus, and the tail from the axial
filament and nebenkern. While I do not deny the presence of a middle
piece, my observations do not warrant me in describing one, although
fig. 40 would suggest it.