The spermatogenesis of Hydra. 401 
which lay at one end of the nucleus has disappeared. Again the 
nucleus changes its shape, becoming spheroidal. The half turns of 
the spiral thread of chromomeres become meridians. * Segmentation 
of the thread occurs at the poles, and the nuclear membrane disap- 
pears. The segments of the spireme thread contract forming an 
equatorial plate of nearly spherical chromosomes. Two centrosomes 
now appear over the poles and therefore 90° from the point at which 
the centrosome disappeared. A thread from each chromosome grows 
to each centrosome, or through it to the cell wall. Division is an 
equation division for each daughter chromosome contains four chro- 
momeres, the same number as the parent chromosomes (Fig. 44 and 
45). The late anaphase and the telephase do not differ from those 
already noted for the spermatogonia. In the late telephase the 
nucleus stained with iron haematoxylin takes a deep blue black color 
and frequently has a collapsed appearance (Fig. 46). Occasionally 
the color settles in spots and rings (Fig. 47). While the nucleus 
stains similarly with safranin, yet being a transparent stain the 
chromomeres can still be seen. In the majority of cases 24 are 
visible. Yet in some cases where it seemed hardly possible that any 
were hidden, fewer than twenty-four could be counted. 
Mitosis in the spermatocytes of the second order. 
It is in this division of the spermatocytes of the second order 
that the details of division have been most carefully worked out. 
These cells are sufficiently small to be usually all included within 
the thickness of a single section, whereas the spermatogonia were 
much more likely to have part of the mitotic figure cut away in the 
next section. The chromomeres during the late telephase of the first 
spermatocyte division become connected by linin strands, but do not 
form the fine meshed reticulum of the resting nucleus (Fig. 49). 
Prophase. 
The early prophase of the division of the spermatocytes of the 
second order is marked by the disappearance of all these connecting 
strands except one between each two adjacent chromomeres, thus 
forming a continuous beaded thread irregularly coiled (50). 
Spireme. 
As in the spermatogonic division the daughter cells after the 
division of the spermatocytes are polyhedra with the centrosome 
