AND OF HYBRID PIGEONS. 
33 
4. Sixteen loop-shaped chromosomes occur in the sper¬ 
matogonia. They split longitudinally in division. 
5. The last division of the spermatogonia results in the 
production of cells which, through a process of growth, become 
the primary spermatocytes. 
6. Synapsis occurs in the primary spermatocytes through 
which a pseudo-reduction of the chromatin takes place. In the 
division of the spermatocyte only eight chromosomes appear, 
but they are in the form of heavy rings or vesicles and are evi¬ 
dently bivalent. 
7. During the synaptic phase there is a marked drifting 
of the chromatin to the side of the nucleus in contact with the 
sphere. Some of the contents of the nucleus apparently pass 
out into the sphere. 
8. During division the eight chromosomes which are in¬ 
cased in capsules of linin break transversely, and as they move 
apart they remain connected by threads of the linin casing. 
These threads form the interzonal fibres. 
9. Intermediate bodies at the equator of the interzonal 
fibres are present after all divisions. 
10. The secondary spermatocytes result from the division 
of the primary spermatocytes. Some, at least, go into a resting 
stage, but it is of very short duration. 
11. In the division of the secondary spermatocytes only 
four chromosomes appear. They are of the same size and 
shape as those of the preceeding division. It is suggested that 
they are quadrivalent. 
12. If chromosomes are to be considered as differentiated 
into qualitative areas, then a qualitative reduction apparently 
occurs. It is possible that the chromosomes of the secondary 
spermatocyte are quadrivalent. This would probably result in 
a greater amount of variation in the offspring than would follow 
from the division of an ordinary bivalent chromosome. 
17. In the transformation of the spermatid, the first per¬ 
ceptible change is in the centrosome. It divides and one of the 
resulting centrosomes enlarges and becomes ring-shaped. 
18. The axial filament of the tail first appears as a thread 
connecting the two centrosomes and later continues backward 
through the ring-like centrosome and out of the cell. 
