618 Gro. W. TANNREUTHER, 
the first spermatocyte division the chromatin granules collect at 
definite points and form a distinct spireme (Fig. 77—78). The 
spireme shortens (Fig. 78—80) and the chromatin masses at different. 
points on the spireme (Fig. 81—83). This process continues until 
the six definite chromosomes are formed (Fig. 84—86). There is no 
nuclear membrane formed but the nucleoplasm is distinctly clearer 
than the cytoplasm. There is apparently no fusion of chromosomes 
during the growth period. The somatic number six is found in the 
prophase of the first spermatocyte division. The chromosomes unite 
end to end in the prophase of the first spermatocyte division 
(Fig. 87—88). The four large form two pairs, and the two small 
chromosomes one pair. These fused pairs of chromosomes have the 
same characteristic shape as the single chromosomes except that 
they are larger (Fig. 89). The three bivalent chromosomes are 
arranged in an equatorial plate and the nuclear and cytoplasmic 
areas are distinct (Fig. 90). There is no definite achromatic spindle 
formed, but in the early metaphase (Fig. 91), as the chromosomes 
divide, they remain connected at a common center or point by 
thread-like fibers, which have the same affinity for stain as the 
chromatin (Fig. 92). In passing from the metaphase to the telo- 
phase these fibres become more united and form a common inter- 
zonal mass of fibres (Fig. 93—96). In the late telophase these 
fibres loose their immediate connection with the chromosomes (Fig. 95), 
but persist in the cytoplasmic area after the spermatocytes have, 
completely divided (Fig. 97). There is a short resting stage before 
the second spermatocyte division (Fig. 98). The first maturation 
or spermatocyte division separates paired chromosomes. The spermato- 
cytes of the second generation have three chromosomes, two large 
and one small (Fig. 99). In the second spermatocyte division, the 
interzonal fibres exist as in the first, but play no part in the 
formation of the sperm. The early transformation stages of the 
spermatids before the cytoplasm begins to elongate are shown in 
Fig. 107—110. 
The nucleolus first appears after the last spermatogonial division 
at the beginning of the growth period. It is found in its earliest 
stage in the center of the chromatin area (Fig. 76). It has the 
same affinity for stain as the completely organized chromosomes. 
Before the chromosomes become distinct the nucleolus passes to the 
periphery of the nucleus and divides (Fig. 82). Or as in some 
instances, it divides before passing to the periphery. The nucleolus. 
