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Transactions of the Society. 
the result of an upeurving of the outer ends of the divergent halves 
of the mother-chromosomes. But I have been myself led to a different 
conclusion, as the result of my own studies on this plant, and a com- 
parison of it with other species of Lilium. The main assumption 
which underlies Miss Sargant’s argument seems to be that the original 
chromosome splits longitudinally, and that the two halves then diverge 
as simple bars. These may subsequently become bent, but the curved 
form is of secondary importance. She further implicitly concludes 
that the relative lengths of the divergent ends and the as yet unsplit 
portion (of the original chromosome) will furnish a criterion of the 
age, or stage of development, to which that body may have attained. 
I think that the assumption as to the mode of splitting and also the 
conclusion as to the age need proof, and I further believe that, as 
a matter of fact, the whole process really takes place in a manner 
other than that which has hitherto been considered to be the mode. 
If the genesis and early steps in the development of the chromo- 
somes from the resting nucleus be followed out, the process will be 
found to be as follows, though variations from the normal type fre- 
quently occur. 
1. Normal type. — As the linin framework of the nucleus becomes 
more prominent, it shortens and thickens, and the tangled skeinwork 
becomes more and more unravelled. Chromatin appears in it, but is not 
uniformly distributed. As the nucleus proceeds through its changes, 
the linin thread flattens, and the chromatin is especially abundant 
at its edges ; furthermore, at certain entire transverse areas it is nearly 
absent. These spots mark the places where the original filament will 
split transversely into its twelve segments. Along with these changes 
the linin is seen to split longitudinally along its middle line, from 
which the chromatin is nearly or quite absent. This is the longi- 
tudinal fission referred to by authors. Now it has always been 
assumed that the remaining steps in the formation of the daughter- 
chromosomes, which arise by the separation of the longitudinal halves, 
consist in their simple divergence, though only after a somewhat 
considerable interval of time. This, however, seldom corresponds 
with the true state of the matter. A certain number of the twelve 
chromosomes (formed by the transverse breaking up of the filament, 
as above described) are still seen to be completely split horizontally. 
Many of them, however, are only cleft along the middle, and are 
closed at one or both ends, thus forming closed links, or ellipses 
— the closed rings of Flemming’s figures. 
As the process of mitosis progresses, the twelve segments are 
seen to be distributed just within the wall of the nucleus, and to 
assume, in many cases, a curved form. They then, almost suddenly, 
retreat to the equatorial plane of the nucleus, and this happens 
concomitantly with the formation of the achromatic spindle. At 
this stage the number of ellipse-shaped chromosomes is relatively 
increased , and I regard this as the result of the fusion at the ends, 
