THE MAIOTIC PROCESS IN MAMMALIA 
83 
At a somewhat later stage the loops assume the arrangement given in 
(Fig. D). They each consist of a long twisted thread, all ending a few com- 
posite chromatin centres that have arisen through the amalgamation into 
groups of those previously scattered through the nucleus. 
The thread consists of linin, along which the chromatin is scattered in 
the form of irregular granules, as shown in the figure. There is no trace up 
to this stage of any longitudinal splitting in the thread work. In (Fig. D), 
however, we have a somewhat later stage than (Fig. C). In this the loops are 
still seen to radiate from composite chromatic centres, but these are now 
breaking up again. And in some loops it will be seen that the chromatin is 
now distinctly arranged in two rows. The loops are, in fact, in the act of 
assuming the well-known double beaded appearance. 
There is no more doubt in the case of these mammalian cells than there 
is in those of Triton that the double beading of the threads arises through a 
separation of the chromatin along each individual thread into two rows. But 
it is questionable whether each of the chromatin granules divides, or whether 
they gradually become arranged in this manner. 
At a later stage (Fig. E) the chromatin centres become separated up, and 
each is now seen to consist of the peripheral ends of the individual loops. 
The double, or split, condition of the thread now extends from end to 
end of the loops, and this gives to each end, or chromatin centre, on the 
nuclear membrane, a new appearance of being double. 
A later stage is represented in (Fig. F). The double or split nature of 
the chromatin is still seen. The loops are, however, shortening up to form 
the adult gemini. 
In (Fig. F) it will be seen that these loops are often clearly divided in the 
middle. Thus at this stage each loop consists of two lengths joined by their 
ends, and each length is split longitudinally from end to end. 
In the guinea pig there are, as we have seen, 32 pre-maiotic chromo- 
somes, and the synaptic loops of the first maiotic division resolve themselves 
into 16 gemini, so that we are led to conclude that gemini consist each of two 
somatic chromosomes joined end to end. This conception is fully confirmed 
by the observations we have made upon the synapsis in Triton, where the 
coupling up of the pre-maiotic chromosomes can actually be seen during the 
pre-synaptic rest. 
During the time that the coarse spirem is breaking up to form the sixteen 
synaptic aggregates, remarkable changes go on in relation to the constituents 
of the attraction sphere. During the synaptic contraction it will be remem- 
bered that the centrosomes lay at the centre of an enlarged archoplasmic mass 
as in (Fig. 14). But at stages such as those represented in (Figs. 18, 19, 20, 
2i), it is found that the centrosomes migrate outwards from the archoplasmic 
centre to the surface of that body as in (Fig. 18). Still later they are en- 
countered completely outside the archoplasm, as in (Fig. 20), and at this time 
it is often noticed that one or both of these bodies has divided, as in (Fig. 21). 
About the same time it is in some cases — in the guinea pig — possible to 
discern that from each of the centrosomes there proceeds a delicate 
protoplasmic thread of extreme tenuity, and only visible if the preserva- 
