34 CARL G. HARTMAN 
Three more or less distinct regions are typically recognizable 
in many of the ova (fig. 12, pl. 14). There is a marginal zone, 
sometimes very narrow, consisting of granular cytoplasm, 
nearly devoid of fat granules. Beneath this is a more or less 
diffuse zone of oil globules, which may be very small or very 
large or medium in size, as seen from the figures on plate 14. 
Some litters show considerable uniformity in this respect (No. 
76) and in others there is variation within the litter (No. 313, 
figs. 12 and 18, pl. 14). The outer surface of this zone of fat 
globules is often marked by a delicate region which may break 
down in fixation (light zone in figs. 12 and 19), reminding one 
of the delicate deutoplasmic pole of the egg of Dasyurus. In 
the living opossum egg this region is a light band interrupted 
here and there with oil globules coming near the surface. The 
third region is the large central portion of the egg which is 
rather uniformly granular and contains few oil globules or 
vacuoles. 
The tubal ovum, like the ovarian ovum, exhibits no polar 
concentration of yolk, which is in striking contrast to the un- 
segmented ovum of Dasyurus, in which the deutoplasm is 
gathered in a mass at the vegetative pole of the egg and is 
bodily extruded just prior to the first cleavage; whereas in the 
opossum the yolk is thrown out from both ends or from all sides 
in greater or less amounts, as the sequel will show. 
4. The polar body. The first polar body, which is present in 
all ripe ovarian eggs and in all tubal ova, lies in a spindle-shaped 
depression under the vitelline membrane. It is never large, 
containing a modicum of cytoplasm, in contrast to the prodigality 
with which yolk and cytoplasm are eliminated from the egg in 
cleavage. The polar body is usually of such a peculiar color 
and homogeneous texture that it is easily recognizable in eggs 
fixed in Bouin’s fluid; but if the fixing fluid contain osmic acid 
the polar body is seldom recognizable. The chromatin is 
usually a deeply staining irregular mass. 
Both polar bodies are soon absorbed, disappearing as dis- 
tinctive structures in early cleavage. Except for a slight differ- 
ence in size, the two polar bodies are practically identical. I 
