No. 3-] UTERUS AND EMBRYO. 407 
ker and Langhans, the former designating them as the chorionic 
epithelium, while the latter doubtfully traces their origin to 
the uterus. That Kolliker (Entwickelungsgeschichte, 2te Aufl., 
p. 322) is right, I am confident. It is easy to follow the layer 
of cells in question at the edge of the placenta, and see that it 
is directly continuous with the cellular layer of the frondosum, 
which it resembles in character. On the other hand, the ecto- 
Cut 24. — Placenta at full term. A, vertical radial section through the margin; 
D, decidua; v2, aborted villi outside the placenta; Cho, chorion; .Sz, circular sinus; 
V2, placental villi; 724, canalized fibrine. B, portion of A more magnified to show 
the decidual tissue near 4; wv, blood-vessel; ad’, decidual cells; d@, with one, @’, 
with several nuclei. 
dermal cells of the lave are distinct in character from the decid- 
ual cells next to them, Cut 34, having smaller and more darkly 
stained nuclei, and much more coarsely granular protoplasm ; 
the ectodermal cells are much smaller than the decidual. The 
ectoderm is sharply marked off from the decidua, but its surface 
