324 Mottier . — The Development of the Heterotypic 
Soon after the stage shown in Fig. 10, the chromosomes separate and 
become more or less scattered within the cavity of the nucleus. The seg- 
ments of the chromosomes (i. e. the two chromosomes of the bivalent 
structure) are variously oriented toward each other. They may still adhere 
as a loop, as an open or closed ring or link, as straight thick rods lying 
closely side by side, or attached end to end. They may or may not 
be twisted upon each other. These and various other dispositions of 
the segments toward each other may be observed in all stages from the 
time of complete cross segmentation of the spirem to the mature spindle 
(Figs. 11, 12, 13, 14). In Fig. 14 are shown a few of the various forms of 
chromosomes observed in the spindle. Of these, that of Fig. 14# is less 
frequently observed. The arrangement of the two segments toward each 
other doubtless depends on the manner in which the spirem was looped or 
entangled at the time of cross segmentation. So far as the writer can see, 
no special significance can be attached to the various orientations of the 
two segments toward each other. 
Now, when we take into account the development of the chromosomes 
of the heterotypic mitosis from the hollow spirem, but one conclusion seems 
possible, namely, that each chromosome appearing in the equatorial plate 
of the spindle is bivalent, consisting of two chromosomes that were disposed 
end to end in the spirem ; that the two segments of the whole chromosome 
are not daughter segments but two somatic chromosomes. From what 
is known during the anaphase, it is clear that each of these segments, 
or somatic chromosomes, is in turn double, consisting of two daughter 
segments which arose by the longitudinal splitting seen immediately 
following synapsis. Each bivalent chromosome may, therefore, consist 
of four chromosomes, each member of the bivalent chromosome consisting 
of two daughter segments. Consequently the first mitosis is a reducing 
division, that is, the numerical reduction of the number to one-half is 
accomplished, one-half of the somatic chromosomes going to one daughter 
cell and the other half to the other. 
Lilium . In the period of the prophase of LiUum, between that 
following synapsis and the transverse segmentation of the spirem, certain 
details are more complicated and may lead more readily to different inter- 
pretations. For example, in two closely related stages, it is frequently 
difficult to determine which is younger or older, and a careful study and 
comparison of the figures of the several observers seem to indicate that 
older stages in the prophase have been interpreted as representing earlier 
steps in the process. Such errors, although slight, are sometimes sufficient 
to throw the observer’s judgement against the conclusion that all other facts 
seem to support. 
As pointed out in a preceding paragraph, the loose spirem, following 
synapsis, and which is longitudinally split, soon reaches its stage of greatest 
