PATHOLOGIC OVA, ALBINO RAT 361 
It is my primary purpose to make records of the abnormal ova 
observed in the material at hand; and to follow these records with 
a brief consideration of the observations made. There is no 
literature dealing with the problem immediately at hand—abnor- 
mal rat ova. It is not my purpose at this time to enter into the 
extensive literature of comparative experimental teratology. 
This has been critically summarized relatively recently by O. 
and R. Hertwig, and by Mall, in his several contributions deal- 
ing with human pathologic ova. 
HALF EMBRYOS IN MAMMALIA 
The first preparation to which attention is called is one taken 
from the oviduct of rat No. 60, 1 day, 18 hours, after insemina- 
tion. The two oviducts of this rat contained seven ova in the 2- 
cell stage, to one of which especial attention was drawn in Part I 
(page 271). As there recorded, in one of the 2-cell stages, the 
first two blastomeres were separated by an appreciable distance. 
There is loss of oolemma. The possibility of half embryos in 
Mammalia was suggested. The preparation under consideration 
is figured in figure 1, A and B. In A of this figure there is pre- 
sented a portion of the wall of the oviduct, its epithelal lining 
and the immediately adjacent mucosa, including the fourth of a 
series of six sections (10 uw) passing through the two blastomeres. 
In this region, the cilia of the epithelium are clearly observable, 
as may be seen from the figure. In B of this figure there are 
sketched in approximately relative position the several sections 
of the series passing through the two blastomeres, the relative 
position of which, with reference to the walls of the tube, is shown 
in A of the figure. The six drawings were made from a well 
ribboned series; the slide was moved from section to section by 
means of a mechanical stage, and the perpendicular indicated on 
each drawing as made. The relative position of the several 
drawings, therefore, is quite correct. It may be observed that 
throughout the series the two blastomeres are separated by an 
appreciable space, and that one of the cells has rotated slightly 
on its axis. If these two blastomeres had remained in close appo- 
sition, they would present the appearance of a normal 2-cell stage 
