THE MAIOTIC PROCESS IN MAMMALIA 
79 
PRE-MAIOTIC DIVISION. 
When a pre-maiotic cell is about to divide the nucleus becomes finer in 
texture, and more readily stainable. The coarse granules disappear, and are 
replaced by evenly distributed, finer, particles. The alveolar structure of 
the nucleus becomes subsequently coarser and coarser, so that the lining 
eventually takes on the appearance of a much-contorted ribbon, or ribbons, 
along which the chromatin is spread. (Fig. 2.) This figure, the so-called 
spirem, does not follow, as it were logically from the breaking up of the 
preceding network ; but the nuclear contents assume their new form in an 
arbitrary fashion ; for which at present we cannot account. In some cases 
the spirem has the appearance of a coiled and endless filament ; in others this 
is never fully attained. In any case, however, the spirem stage is succeeded 
bv a phase in which the thick thread work has broken up into a number of 
segments, as in Fig. 3. In all animals and plants the number of such seg- 
ments, or chomosomes, is apparently constant, for any particular form, and in 
mammals this number is thirty-two in man, rats, and guinea pigs, twenty-four 
in mice. 
While the above intra-nuclear changes are going on, others proceed in 
the cytoplasm. The centrosomes become more conspicuous, and are sur- 
rounded by fans of radiations, while eventually they separate from one 
another with great rapidity, and take up positions on opposite sides of the 
nucleus. Sometimes in the pre-maiotic division of mammals it is at this 
period observable that the chromosomes are apparently split longitudinally ; 
but this cannot generally be seen until a later stage. At about the same 
time the nuclear membrane becomes irregular and disappears ; the clear 
nuclear substance often remaining as a light space round the liberated 
chromosomes. 
The radiations round the centrosomes raoidly increase, extend across 
this intervening space, and become fixed upon the chromosomes themselves, 
these bodies gradually taking up an equatorial position, still adhering by their 
middles to sheafs of spindle fibres. (Fig. 5.) At this period in the guinea-pig 
it becomes possible to make out that the bent, rod-like chromosomes are 
longitudinally split, and as the mitosis proceeds the two halves of each 
chromosome are gradually drawn away from one another towards the centro- 
somes. (Fig. 4.) Here they collect 111 a couple of irregular masses of V 
shaped daughter elements, which are at first arranged in the form of rings (or 
diasters), the centrosomes lying immediately beyond them. (Fig. 6 and 7.) 
In a short time the daughter chromosomes become vesiculate, and run into 
one another, so that eventually they form an irregular nuclear mass at either 
pole of the dividing cell. (Fig. 7.) These daughter nuclei become eventually 
surrounded by new membranes, and the centrosomes pass along a groove 
round their surfaces towards the original equatorial face of each. At the 
same time the whole cytoplasmic mass of the dividing cell becomes hour-glass 
shaped, and this character increasing, the cell divides into two, a small 
residuum of the substance forming a portion of the spindle which originally 
intervened between the separating chromosomes remaining visible in either 
cell, and apparently going to form the condensed mass round the centrosomes, 
or archoplasm. (Fig. 9.) 
