96 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
lying within the cytocoel. As the spermatid elongates into the sper¬ 
matozoon, the cortical cytoplasm of the spermatid becomes elongated 
into a narrow tube, the lumen of which is bounded by the original 
cytocoel. Into this lumen, the cytoreticulum of the central portion 
of the cell becomes compressed till it looks like a mere fiber. Thus, 
if the cell represented in figure 125 (pi. 17) were pulled out lengthwise 
to many times its original length would there not result some such an 
effect as in the cell represented in figure 143 ? 
Comparing the mass of the spermatid with the mass of the fully 
developed spermatozoon (pi. 17, fig. 149), there is no ground for 
supposing that the transformation of the spermatid into the sperma¬ 
tozoon involves an actual increase in the quantity of protoplasm. 
The comparative inertness of the nucleus at the close of the last 
maturation division and ever afterward (already considered) would 
not justify us in assuming that this is a growth period primarily in 
the history of the spermatozoon; but rather that it is a transformation 
period of those organs that are already present and fully grown in the 
spermatid stage. This transformation in all the organs of the cell is 
merely an elongation such as could be brought about, doubtless, by 
prolonged equal lateral pressure. 
Fate of the nehenkern .— My interpretation of the spermatozoon as 
being in a sense a tube formed by the cortical cytoplasm, and contain¬ 
ing the axial filament representing the greatly attenuated central 
cytoreticulum of the original spermatid, is supported by some other 
considerations to be noted regarding the fate of the nebenkern. 
The nebenkern has nothing to do with the middle piece of the 
spermatozoon. Originally the nebenkern always occupies the position 
where one would naturally expect the middle piece to develop. In 
this position it remains, too, for some time. Its size apparently varies 
with the size of the cell. Compare the small spermatids (pi. 14, fig. 
40; pi. 17, fig. 126-130) with the giant spermatids (pi. 14, fig. 46; 
pi. 17, figs. 131, 138). It can be readily seen even in unstained sections. 
Its staining reaction is cytoplasmic. Its first appearance reminds 
one forcibly of the cytoplasm of the grandmother stem cell. Like it, 
too, it is remarkable for its resistance to nuclear stains. It stains, as 
does the grandmother cell, in saffranin and acid fuchsin. In the large 
spermatids, especially, it is often many times the size of the nucleus, 
and apparently perfectly spherical. At first, homogeneous and re¬ 
sembling archoplasm, it gradually becomes more granular, and as the 
