136 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
The very slight attachment of the ovum to the decidua thus seen has also 
been demonstrated by Fothergill, who described a very . early ovum which was 
expelled with a decidual cast. 
The ovum, which was a small yellow body, about the size of a ' split pea,' 
was found on a plug which had been used to pack the vagina, but no trace of its 
resting-place was to be seen in the cast. 
Sections of the decidua showed the usual typical structure. The uterine 
epithelium remained unaltered in the deep layer of the decidua, but the glands were 
dilated and had lost their epithelium in the middle and superficial layers. There were 
large decidual cells and numerous spaces filled with fresh blood. No chorionic vil.i 
or portions of chorionic epithelium were visible. 
Examination of the small yellow body showed a complete ovum about a half 
centimetre in diameter, consisting of a sac of chorion only, completely covered with 
chorionic villi. No traces of an amnion or germinal area were found. Fothergill 
believes that this specimen had not grown for more than five or six days. 
In October, 1901, a similar cast was handed over to me for investigation, 
which proved of great interest, in that it revealed an ovum, corresponding in many 
respects to that of Peters. The specimen (see Fig. 1, Plate VIII) shows a very perfect 
decidual cast. It has three openings, one corresponding to the os, the remaining two to 
the openings of the Fallopian tubes. The anterior surfaces had a flattened appearance, 
while the posterior was rounded in contour, the whole being shaggy and slightly 
nodular. It had been spontaneously expelled from a patient who had missed one 
period and who was suffering from retroflexion. On examining the external appear- 
ances of the specimen, attention was first called to the anterior and upper surface by 
a slightly pale area. This was carefully incised and found to be the site of a complete 
ovum, embedded in the decidual tissue. It measured 5 mm. in its longest diameter 
and 4 mm. in its shortest. 
On section, the decidua appeared very much the same as that described in 
Fothergill's case, and enclosed the ovum completely, except at one point only, 
demonstrable under the microscope, where the decidua capsularis was wanting. (It is 
believed that, at this point, the fertilized ovum burrowed its way into the maternal 
tissue). Well-formed villi are seen surrounding the chorionic vesicle (see Figs. 2 and 3, 
Plate VIII), but even at this early stage thev are more numerous at the point opposite 
the decidua basalis. The epithelium covering the villi has, in many places, retained its 
primary trophoblastic form, in this respect, closely resembling the cells found in 
Peters' ovum, and is seen forming a distinct connexion between the ovum and the 
maternal wall. In most of the villi, the trophoblast forms a single investing covering, 
which shows the syncytium with numerous buds in the outer layer, and a more 
definite inner row of cubical cells, the ' Zellschicht ' of Langhans. In several of 
the sections a distinct embryonic area is seen, composed of an irregular mass of 
