AND OF HYBRID PIGEONS. 
11 
mass may persist as a distinct body in the nucleus during the 
preparatory rearrangement of the chromatin for division (Fig. 
4, 1.), but it usually takes part, together with the network, in 
forming the achromatic sheath or covering within which each 
individual chromosome is incased. 
Before division the nucleus passes from the so-called resting 
condition through an incomplete spirem stage. The spirem is 
formed through the rearrangement of the chromatin and linin 
material. The chromatin is laid down in minute granules, and 
these begin to spread out from the various chromatic dots and 
clumps through the linin substance which forms a sort of cover¬ 
ing or case for them. If the saffranin gentian violet method 
has been employed in staining, the linin is of a reddish violet 
color and the chromatin granules deep red. As the granules 
extend out more and more along the violet threads, the latter 
become redder and redder, until in the final condition of inde¬ 
pendent chromosomes, each chromosome appears as a red loop 
or thread. A very close examination under high power reveals 
the fact, however, that the red part of the chromosome is sur¬ 
rounded by a thin violet colored layer of linin (Fig. 4). 
At first the newly formed chromosomes lie scattered irreg¬ 
ularly throughout the nucleus, but later, just before the spindle 
is formed and the nuclear membrane disappears, they arrange 
themselves around the periphery. Sometimes the nucleolus of 
linin-like material persists and is visible lying more towards the 
center of the cell (Fig. 4, 1.). With the transformation of the 
spirem into chromosomes there is also an increase in the vol¬ 
ume of the nucleus. 
In the last division of the spermatogonia before they un¬ 
dergo growth to form spermatocytes there is a curious casting 
out of part of the chromatin into the cytoplasm while the 
chromosomes are yet in an ear ly stage of formation. After the 
spirem breaks up into individual chromosomes, the latter are 
visible as irregular threads and loops scattered throughout the 
nucleus. They appear later as small rods or loops which are, 
perhaps, elongated vesicles with an internal shell of chromatin, 
judging from the fact that they frequently have the appearance 
of a lengthened ring. Amongst this colony of loops and rods 
there is always one chromatic mass that differs very much from 
