286 Chromosomes in the Spermatogenesis of Anasa Tristis 
throughout the nucleus. In Photo. 3 it is elongated in form, but there 
can be no doubt that it is the same structure. Photos. 5 to 12, Plate I, 
show it still persisting during the stage when the chromatin is assuming 
the form of a reticulum, skein, and chromosomes. In Photo. 10, long 
thread-like chromosomes with a longitudinal split are clearly shown, and 
at the upper right hand corner of the nucleus the persisting plasmosome 
can be seen, though its form has been somewhat disturbed by the tech- 
nique. Photos. 12 to 15 demonstrate the persistence of the plasmosome 
through the later stages, while the chromosomes are assuming their defi- 
nite form, and Photo. 16 shows (at the right of the uppermost chromo- 
some), the latest stage in which we find the plasmosome persisting. At 
these stages it is only faintly defined (as shown in Photo. 16) and when 
the chromosomes have attained their definite form the plasmosome has 
entirely disappeared—thus, in its morphology and time of disappearance 
it closely resembles a typical plasmosome. 
As stated in our preliminary, we have not been able to find a structure 
in the resting spermatocyte, which we feel justified in interpreting as 
the homologue of the accessory nucleolus of the egg. Although we do 
sometimes find a small inconspicuous nucleolar-like body, in addition 
to the plasmosome, its presence is too inconstant to lend support to any 
speculation as to its possible identity with the accessory nucleolus of 
the egg. This small dense body is shown in Photo. 2, Plate I, below and 
to the right of the plasmosome and it is also differentiated in Photo. 5, 
below and to the right of the plasmosome. One is present also in Photos. 
6 and 10, but we fear they are too inconspicuous to be brought out in the 
reproductions. 
In all cases in which both a chromosome nucleolus and a plasmosome 
have been demonstrated in the first spermatocyte of Anasa tristis, the 
chromosome nucleolus has been represented as the more dense and 
more deeply-staining body of the two (for example, see Text Figs. 1 and 
2). Morphologically, it resembles a nucleolus much more than it re- 
sembles a chromosome, and in fact, its morphological likeness to a nucleo- 
lus has been effectively used by Wilson in differentiating it from the 
chromosomes during the prophases, thus proving its identity with the 
chromosome nucleolus of the growth period. The force of this evi- 
dence is shown by a comparison of Wilson’s Fig. a (Text Fig. 1) and 
Photo. 17, Plate I. The latter is a reproduction of Wilson’s (05) sketch 
b, Fig. 2, reduced to a magnification of about two thousand diameters. In 
this section (Photo. 17) Wilson shows the plasmosome () still persisting 
and in addition to this the dense chromosome-nucleolus (h)—the struc- 
ture which he interprets as a persisting, odd spermatogonial chromo- 
