PATHOLOGIC OVA, ALBINO RAT 367 
lobules of the same nucleus. In A of this figure there is shown 
to the lower left of the large cell another relatively large cell, 
enclosing a globular inclusion, which stained faintly, and the 
nature of which was not fully determined. In the upper part of 
each of the two figures are seen cells which show cytolysis and 
loss of nuclei; regarded as degenerating cells. When compared 
with the normal blastodermic vesicles obtained from the same 
uterus, the ovum here described presents a unique appearance, 
and was readily recognized as showing development and structure 
which deviated from the normal. At this stage of development, 
the blastodermic vesicles of the albino rat are still found lying 
free in the lumen of the uterus, showing no structural relation to 
the uterine mucosa. This vesicle has been interpreted as show- 
ing irregular or retarded segmentation. It is conjectured that 
one of the cells, perhaps of the 8-cell stage, did not undergo 
further cleavage. The large cell presents an appearance evidenc- 
ing beginning stages of degeneration, and in further development, 
would probably have undergone dissolution. The majority of 
the smaller cells of the roof appear as if normal, as do also the 
cells of the floor, certain of the smaller cells of the floor presenting 
mitoses as evidence of further proliferation. 
In figure 4, A, B, and C, there are presented typical sections 
of three ova of the albino rat showing what has been regarded as 
irregular segmentation. A of this figure represents an ovum 
taken from rat No. 64, 4 days, 14 hours, after insemination, in 
the uterus of which there were found five normal ova showing 
early stages of blastodermic vesicle formation, four of which are 
cut longitudinally, one in a series of cross-sections. In each of the 
four longitudinally cut series the floor of the respective vesicles 
is markedly folded, owing to fixation contractions; therefore, 
none were sketched as normal stages. * In appearance, they re- 
semble closely the vesicles sketched under C, D, and E of figure 
20, Part I. In the pathologic ovum, shown in A of figure 4, 
there is no evidence of segmentation cavity formation. How- 
ever, the ovum cannot be regarded as presenting a late morula 
stage such as is figured in A of figure 20, Part I, since it shows 
distinct departure from the normal. The marked constriction 
