The nuclear components of the sex cells of four species of cockroaches. 487 
liuin and chromatin can be made. However, with care, it is possible 
to obtain fairly consistent results. None of tbe other stains was 
found serviceable to ideutify the plasmosome, for tbat body absorbs 
tbe chromatin dye so readily tbat the counterstain, ordinarily demon- 
strating plastin structures, will not displace the earlier stain. Thionin 
is useful as affording means of distinguishing tbe plasmosome from 
tbe cbromosome nucleolus of tbe earlier stages of tbe first spermato- 
cyte. In other stages, however, it fails to act in tbis way. Gross’s 
method is applicable in some instances, but not in others. Tbe same 
may be said of the safranin — Lichtgrün combination, while Dela- 
field’s hematoxylin and Heidenhain’s iron-alum method bave not 
been of any value for differentiation inasmucb as tbe plasmosome 
stains intensely in the logwood dyes and will not receive tbe 
counterstain afterwards. 
Observations. 
The observations of the writer will be given in tbe following 
sectiou and in a later portion of tbe paper, comparisons will be made 
with tbe works of others. Periplaneta americana bas been made tbe 
b,asis of tbe .study, the three other species serving- as comparisons. 
Consequently, in the descriptions to be given, tbe spermatogenesis of 
Periplanetci will be given in detail and in tbe account of tbe three 
remaining species, Leucophcea, Stylopyga and Blatta, only the points 
of special interest will be touched lipon. Tbe ordinary cbromosomes 
will be considered first in eacb case, tbe odd chromosome next and 
finally tbe bistory of the plasmosome of each mitosis will be traced. 
Periplaneta americana (L.). 
1. The spermatogonia and oögonia. 
a| Tbe cbromosomes of tbe male. Spermatogonia occur in at 
least two series in tbe testis of tbis species. Tbe earlier ones bave 
larger cbromosomes (fig. 1) than the later series (fig. 4) and tbe nu- 
cleus as a wbole is larger in the former. It bas been a difficult matter 
to determine, accurately, tbe number of cbromosomes owing to their 
crowded condition in the metaphase plate. However, in six cases, 
where the chromosomes were separated from one anotber, tbe writer 
bas found, clearly, tliirty three. Of these cases, four belonged to 
the primary or early series, while the rest were secondary or later 
