A STUDY IN CHROMOSOME REDUCTION. 607 
the threads have become shorter and thicker than in the previous stages is very obvious. 
This change is further indicated by the frequent appearance of the free ends of the 
double filaments throughout the chromatin mass. 
This shortening and thickening* of the chromatin threads at this early stage 
proceeds with the increasing amount of karyolymph, but when the latter reaches its 
maximum there is a distinct tendency for the threads to spread out and become more 
uniformly distributed throughout the nuclear sap. This feature is brought out in figs. 6, 
7,and 8. This spreading out of the filaments makes it possible to observe more clearly 
the nature of the longitudinal fissure. From these figures it will be seen that the 
fissure does not completely separate the halves of the thread, but takes the form of small 
lacunee, which are much longer than broad, giving the filament a distinctly vacuolated 
appearance. Although these lacunze may be of considerable length and separated from 
one another by short bridges of chromatin substance, they seem not to interfere with 
the fairly uniform thickness of the filaments. As shown in figs. 4 and 5, the two halves 
of the split filament lie almost perfectly parallel to one another. Fig. 4 represents a 
more highly magnified detail of the split thread in the stage shown in fig. 3, and fig. 5 
is taken from the stage in fig. 6. 
Just as figs. 2 and 3 represent transitions from the so-called reticulum to the 
spireme stage, so figs. 6 and 7 represent transitions from the spireme condition to 
condensed chromosomes. Both these changes appear to be nothing more than a 
progressive shortening and thickening of the chromatic filaments. And just as it was 
impossible to say when the reticulum stage ceased and the spireme commenced, so in 
the later stages it is impossible to make a sharp discrimination between the spiremes 
and chromosomes. Under these circumstances I think we may safely regard each 
individual chromatin thread throughout all of these stages as a definite chromosome in 
different conditions of condensation. As a result of a careful and detailed study of 
these reticulum and spireme stages, I find myself quite in agreement with Grégoire and 
other writers, who hold the view that, although the threads may appear vacuolated, 
granular, or even beaded, they are composed of one uniform material. 
In fig. 7 we have represented a stage where the chromatin threads have 
shortened and thickened to such an extent that we may obtain a fair estimate of 
their number. This is made possible because the spiremes have separated from one 
another and are more evenly distributed through the karyolymph. It should be 
noted in passing that this shortening and thickening is of the same nature as that 
which occurs in the earlier stages of the growth period, but later, on account of the 
* The following extracts are taken from my paper on “ The Phase of the Nucleus known as Synapsis””: “ We find the 
chromatin threads slightly thicker and evidently granular, and the interstices between them larger and more clear. This 
would suggest a shortening and thickening but not a contraction.” Then again: “During this process of loosening 
and spreading out of the chromatin into the clear area of the nuclear cavity the threads continue their process of 
shortening and thickening.” 
It is interesting to compare these statements with a more recent extract from Davis’ (1911) paper: “There is no 
question in the writer’s mind but that the events of synapsis are the result of a true contraction, 7.e. a shortening and 
thickening of the strands or threads of the chromatic reticulum.” 
