5O SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
was at one time inclined to believe. Immediately over the band the 
plasma membrane of the cell is invariably strongly indented. The 
cilia which develop from the outer surface of the band in this stage 
are little more than protuberances which seem to strike the plasma 
membrane of the cell and finally penetrate it and grow into mature 
cilia. The band continues to grow in length, but meanwhile decreases 
somewhat in width. It is broadest near the apical end and decreases 
in width gradually at both ends. The elongation continues until the 
band has developed five or six continuous turns around the cell. In 
this mature condition it is found to have developed in the form of a 
helicoid spiral with the apex located at the point of the cell corre- 
sponding to the original position of the blepharoplast. It is thus 
opposite the point of contact of the two spermatids in each case. 
During the growth of the ciliferous band the nucleus of the spermatid 
has increased in size, growing very markedly at the expense of the 
cytoplasm. The entire cell increases in size meanwhile, but not so 
rapidly as the nucleus. 
STRUCTURE AND FORM OF THE MATURE SPERMATOZOID. 
The mature spermatozoids, before they start to swim, differ but lit- 
tle in appearance from the spermatids in the last stage described (fig. 
42). In all cases the two spermatozoids which result from the division 
of the same central cell remain attached together until active motion 
starts. When mature, and before separating, each spermatozoid is 
irregularly hemispherical in shape (fig. 45). The nucleus occupies a 
large portion of the cell, but is plainly surrounded on all sides by a 
layer of cytoplasm. Jhe karyoplasm is coarsely reticular and open, 
and there is almost invariably one or two nucleoli present. The cyto- 
plasm surrounding the nucleus on all sides is very densely granular 
and stains deep violet blue with the Flemming triple process. It is 
so densely granular that it is almost impossible to distinguish the 
reticular structure of the protoplasm. The ciliferous band in the 
mature spermatozoids is plainly shown, forming a helicoid spiral of 
from five to six turns which covers about one-half of the body of the 
spermatozoid. At the apex of the spiral the band apparently leaves the 
surface of the cell and gradually fades out, the small end occasionally 
making a complete but inconspicuous turn in the cytoplasm of the 
cell. At the open end of the spiral the band decreases in width and 
finally fades out entirely. The band retains the shape described in 
the older stages of the spermatid, being distinctly broadest near the 
apical end of the spiral and becoming narrowed to a point at each end. 
The following is the width of the band at each of the six cross sections © 
on one side of a spermatozoid in a median section, beginning at the 
apex of the spiral: 5.1 4,'8.9 mu, 7.7 4, 5.1 4, 5.1 4, 3.8m. . These figures 
would correspond closely with those taken from any other full-grown 
