Helen Dean King 369 
stage of development in the spermatocytes of several of the Urodela. 
Up to the stage of Fig. 14, the chromatin reticulum in the sperm- 
atocytes of Bufo is very fine and one can readily see that the chromatin 
granules are arranged serially. The continuous spireme found at the 
stage of Fig. 15 is always perfectly homogeneous. Although I have 
examined large numbers of spermatocytes very carefully with this partic- 
ular point in mind, I have never been able to find a single cell in which 
there was the slightest evidence of a longitudinal splitting of the spireme 
at the stage of Fig. 15, nor during any stages showing the condensation 
of the nuclear contents. I have already stated that I regard the apparent 
pairing of the chromatin threads shown in Fig. 13, 14, 18, 19, as purely 
accidental. In most cases the parallel threads are some distance apart, 
this would probably not be the case if a longitudinal splitting of the 
spireme had occurred; again, the threads are never connected by fine 
fibres, as is usually the cases with sister portions of a longitudinally 
split chromatin skein; most important of all, during the early stages 
of the formation of the nuclear reticulum, the threads are always com- 
posed of a single series of chromatin granules and they are all of the 
same thickness whether they are single or in pairs. 
Recently several investigators, among whom may be mentioned A. and 
K. E. Schreiner (54), and von Winiwarter (61), have maintained that 
the apparent longitudinal splitting of the chromatin loops during or 
soon after the “ bouquet ” stage is, in reality, a folding together of the 
chromatin filaments so that two of them come to lie parallel and thus 
produce the appearance of a split filament. Synapsis, according to this 
interpretation, is brought about by a side by side conjugation of the 
chromosomes and not by an end to end union. A folding together of the 
parts of the chromatin skein is exactly what occurs in the young sperm- 
atocytes of Bufo at the stages of Figs. 13, 14, 18, 19; but this arrange- 
ment always occurs before the synizesis stage and never after it, and it is 
found in only a small minority of the spermatocytes. Were this pairing 
of the chromatin threads interpreted as a conjugation of univalent chro- 
mosomes that is to persist throughout the synizesis stage and until the 
metaphase of the first maturation division, then, as will be shown later, 
both of the maturation divisions would of necessity be reduction divisions 
and there would be no way in which the individuality of the chromo- 
comes could be maintained from one generation to the next. I cannot, 
therefore, believe that the apparent pairing of the chromatin threads 
in the young spermatocytes of Bufo is of any great importance, although 
I do not question but that it may be a constant and important stage in 
the development of the germ-cells in other forms. 
