A STUDY IN CHROMOSOME REDUCTION, 603 
upon the enveloping plasmatic membrane. The distended and spherical form of the 
nucleus suggests no other interpretation. 
THe GrowrH PERIOD. 
As already pointed out, the chromatin threads, at this early stage of the prophase 
(fig. 1), are evenly and uniformly distributed throughout the nuclear cavity except in 
the immediate vicinity of the nucleoli. With the first indication of the passing of the 
threads from the reticulum stage into the spireme condition, 7.e. when the threads 
become more sharply defined and appear to be shortening and thickening as shown in 
fig. 2, this uniform distribution of the chromatin throughout the nuclear cavity no 
longer prevails. (o-incident with these slight changes in the length and thickness of 
the chromatin threads, there is an evident increase in the amount of karyolymph, and 
the amount of chromatin as indicated by the cubical volume it occupies appears to be 
stationary. 
This is the beginning of what I have in a previous paper (Lawson, 19114) called 
the ‘‘ growth period’”’—a period during which there is undoubtedly a great increase in 
the volume of the nuclear sap, with no corresponding increase in the volume occupied 
by the chromatin substance. In order to more clearly express what is meant by this 
term, and to limit its application, I shall hereafter call it the “ meiotic growth period.” 
This increase in the amount of nuclear sap first shows itself by a slight distension of 
the nuclear plasmatic membrane beyond the outer limits of the chromatin. This 
distension appears in section, as a clear crescent-shaped area between the chromatin 
and the nuclear membrane. The early stages of this have already been fully described 
and figured in my previous paper, and I have no modifications to make in the account 
there given; but by way of confirmation I shall describe and figure one or two of the 
later stages. Figs. 2 and 3 represent such stages. In fig. 2 we see that the crescent- 
shaped area enlarges so as to almost completely surround the chromatin mass. As 
indicated in figs. 3 and 6, the chromatin mass is, as in the great majority of cases, left 
in an excentric position. Occasionally, however, it may be found in a perfectly 
central position with a clear uniform zone of karyolymph completely surrounding it. 
Whether the chromatin mass is left in an excentric or a central position is a matter 
of no consequence. Both effects are brought about, not by the shrinkage or contraction — 
of the chromatin mass—as has been so frequently stated by other writers (Farmer, 1905 ; 
Davis, 1909; Gricorre, 1910; Diesy, 1910; Overton, 1909; and others), but by the 
enlargement of the nuclear vacuole and the withdrawal of the nuclear membrane from the 
chromatin mass. This may be easily demonstrated beyond any question—especially in 
those early stages before thechromatin mass has lost its spherical form—by actual measure- 
ments, or by making one camera drawing upon another on the same paper. In the 
later stages, represented in figs. 3 and 6, this is not so easily demonstrated, because as 
the nuclear volume enlarges, the chromatin mass gradually loses its spherical form and 
becomes very irregular in outline and unsymmetrical, and it is impossible to obtain a 
